Light-emitting elements comprising iridium organometallic complexes comprising aryl-substituted pyrazines

ABSTRACT

Provided is a novel organometallic complex which can be synthesized easily and emits phosphorescence, or a compound which emits red phosphorescence. The inventors focused on easy synthesis of an m-aminophenyl pyrazine derivative represented by the following general formula (G0), synthesized an organometallic complex having a structure in which the derivative is coordinated to a Group 9 or Group 10 metal ion, and further synthesized a useful substance which emits red phosphorescence.

This application is a divisional of copending U.S. application Ser. No.13/333,218, filed on Dec. 21, 2011 which is incorporated herein byreference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to an organometallic complex. Inparticular, the present invention relates to an organometallic complexthat can convert a triplet excited state into luminescence.

2. Description of the Related Art

An organic compound absorbs light, thereby producing an excited state.Through this excited state, various reactions (photochemical reactions)occur in some cases, or luminescence is generated in some cases.Therefore, the organic compounds have been variously applied.

One example of the photochemical reactions is a reaction of singletoxygen with an unsaturated organic molecule (oxygen addition) (seeNon-Patent Document 1, for example). Since the ground state of oxygenmolecules is a triplet state, oxygen molecules do not produce a singletstate (singlet oxygen) when they are excited directly by light. Incontrast, when oxygen molecules interact with triplet excited moleculesother than oxygen, the oxygen molecules form singlet oxygen, resultingin an oxygen addition reaction. Here, the compound that forms thetriplet excited molecules by light and enables formation of singletoxygen is called a photosensitizer.

Thus, formation of singlet oxygen requires a photosensitizer that canform triplet excited molecules by light excitation. However, it isunlikely that a typical organic compound is converted to a tripletexcited molecule because the ground state of the organic compound istypically a singlet state and photoexcitation to a triplet excited stateis forbidden transition. For such a photosensitizer, a compound that caneasily undergo intersystem crossing from the singlet excited state tothe triplet excited state (or a compound that allows forbiddentransition in which the compound is directly converted to a tripletexcited state by photoexcitation) is thus needed. That is, such acompound can be used as a photosensitizer and regarded as being useful.

Furthermore, the above compound often emits phosphorescence.Phosphorescence refers to luminescence generated by transition betweenenergies of different multiplicity. In an ordinary organic compound,phosphorescence refers to luminescence that is generated at the time ofrelax from a triplet excited state to a singlet ground state (incontrast, fluorescence refers to luminescence that is generated at thetime of relax from a singlet excited state to a singlet ground state).Application fields of compounds that are capable of emittingphosphorescence, in other words, compounds that are capable ofconverting a triplet excited state into luminescence (hereinafter,referred to as a phosphorescent compound), include a light-emittingelement containing an organic compound as a light-emitting substance.

An example of a structure of such a light-emitting element is a simplestructure in which a light-emitting layer containing an organic compoundthat is a light-emitting substance is merely provided betweenelectrodes. Light-emitting elements having such a structure can achievethinness, lightweight, high-speed response to signals, low-voltage DCdrive, and the like. Therefore, attention has been directed to thelight-emitting elements as next-generation flat panel display elements.Further, a display including this light-emitting element is superior incontrast, image quality, and wide viewing angle.

The light-emitting mechanism of the light-emitting elements in whichorganic compounds are used as the light-emitting substance is carrierinjection. That is, by applying a voltage with a light-emitting layerinterposed between electrodes, electrons and holes injected from theelectrodes recombine to make the light-emitting substance excited, andlight is emitted when the excited state relaxes to a ground state. As inthe case of the photoexcitation, types of the excited state of organiccompounds include a singlet excited state (S*) and a triplet excitedstate (T*). In addition, the statistical generation ratio thereof in alight-emitting element is considered to be S*:T*=1:3.

At room temperature, a compound that converts a singlet excited stateinto luminance (hereinafter, referred to as a fluorescent compound)emits light only from the singlet excited state (fluorescence), and doesnot emit light from the triplet excited state (phosphorescence).Accordingly, the internal quantum efficiency (the ratio of generatedphotons to injected carriers) in a light-emitting element formed using afluorescent compound is assumed to have a theoretical limit of 25% basedon S*:T*=1:3.

On the other hand, with a light-emitting element formed using a compoundthat converts a triplet excited state into luminance (hereinafter,referred to as a phosphorescent compound), the internal quantumefficiency can be improved to 100% in theory; namely, the emissionefficiency can be 4 times as high as that of a light-emitting elementformed using a fluorescent compound. Therefore, the light-emittingelement formed using a phosphorescent compound has been activelydeveloped in recent years in order to achieve a highly efficientlight-emitting element (see Non-Patent Document 2, for example). Anorganometallic complex that contains iridium or the like as a centralmetal is particularly attracting attention as a phosphorescent compoundbecause of its high phosphorescence quantum efficiency.

REFERENCE Non-Patent Document

[Non-Patent Document 1]

-   Inoue, Haruo, and three others, Basic Chemistry Course    PHOTOCHEMISTRY I, pp. 106-110, Maruzen Co., Ltd.    [Non-Patent Document 2]-   Zhang, Guo-Lin, and five others, Gaodeng Xuexiao Huaxue Xuebao    [Chemical Journal of Chinese Universities] (2004), vol. 25, No. 3,    pp. 397-400.

SUMMARY OF THE INVENTION

An object of one embodiment of the present invention is to provide anovel organometallic complex which can be synthesized easily and emitsphosphorescence. Another object of one embodiment of the presentinvention is to provide a compound which emits red phosphorescence.

The inventors focused on easy synthesis of an m-aminophenyl pyrazinederivative represented by the following general formula (G0). Theinventors synthesized an organometallic complex having a structure inwhich the derivative is coordinated to a Group 9 or Group 10 metal ion,and further synthesized a useful substance which emits redphosphorescence.

Note that in the general formula (G0), R¹ represents any of an alkylgroup having 1 to 4 carbon atoms, an alkoxy group having 1 to 4 carbonatoms, and an alkoxycarbonyl group having 1 to 5 carbon atoms. Further,R² and R³ separately represent hydrogen or an alkyl group having 1 to 4carbon atoms. Furthermore, R⁴ to R⁶ separately represent any ofhydrogen, an alkyl group having 1 to 4 carbon atoms, an alkoxy grouphaving 1 to 4 carbon atoms, a halogen group, a trifluoromethyl group,and an aryl group having 6 to 12 carbon atoms. Further, R⁷ and R⁸separately represent an alkyl group having 1 to 4 carbon atoms or anaryl group having 6 to 12 carbon atoms. In addition, R⁷ and R⁸ may bebonded to each other through a carbon atom, an oxygen atom, a sulfuratom, or a nitrogen atom having a substituent, to form a substituted orunsubstituted five-membered ring or a substituted or unsubstitutedsix-membered ring.

Therefore, one embodiment of the present invention is an organometalliccomplex which is represented by the following general formula (G1) andhas a structure in which an m-aminophenyl pyrazine derivative iscoordinated to a Group 9 or Group 10 metal ion.

Note that in the general formula (G1), R¹ represents any of an alkylgroup having 1 to 4 carbon atoms, an alkoxy group having 1 to 4 carbonatoms, and an alkoxycarbonyl group having 1 to 5 carbon atoms. Further,R² and R³ separately represent hydrogen or an alkyl group having 1 to 4carbon atoms. Furthermore, R⁴ to R⁶ separately represent any ofhydrogen, an alkyl group having 1 to 4 carbon atoms, an alkoxy grouphaving 1 to 4 carbon atoms, a halogen group, a trifluoromethyl group,and an aryl group having 6 to 12 carbon atoms. Further, R⁷ and R⁸separately represent an alkyl group having 1 to 4 carbon atoms or anaryl group having 6 to 12 carbon atoms. In addition, R⁷ and R⁸ may bebonded to each other through a carbon atom, an oxygen atom, a sulfuratom, or a nitrogen atom having a substituent, to form a substituted orunsubstituted five-membered ring or a substituted or unsubstitutedsix-membered ring. Further, M is a central metal and represents a Group9 element or a Group 10 element.

An organometallic complex having the above structure is a compound whichemits red phosphorescence. In addition, the organometallic complex has alow molecular weight, and high thermal stability and sublimationproperty, and thus can be easily evaporated in fabrication of anelement. In general, it is necessary to extend the π-conjugation of alight-emitting material in order to obtain red light emission with highcolor purity, so that the molecular weight of the organometallic complexincreases. As a result, the sublimation temperature of theorganometallic complex becomes higher, and thus evaporation of theorganometallic complex becomes difficult and the organometallic complexbecomes likely to decompose while being evaporated. On the other hand,an organometallic complex according to one embodiment of the presentinvention can provide red light emission with high color purity and hasa small molecular weight, so that the above problems do not arise.

An organometallic complex of an m-aminophenyl pyrazine derivative inwhich an amino group is bonded at a meta position can emit red lightwith high color purity as compared to an organometallic complex of anaminophenyl pyrazine derivative in which an amino group is bonded at anortho position or a para position. In addition, the organometalliccomplex of an m-aminophenyl pyrazine derivative in which an amino groupis bonded at a meta position has a reduced steric hindrance in themolecule and high stability of the molecule, and thus reliability of theelement is increased, as compared to the organometallic complex of anaminophenyl pyrazine derivative in which an amino group is bonded at anortho position or a para position.

Another embodiment of the present invention is an organometallic complexwhich is represented by the following general formula (G2) and has astructure in which an m-aminophenyl pyrazine derivative is coordinatedto a Group 9 or Group 10 metal ion.

Note that in the general formula (G2), R¹ represents any of an alkylgroup having 1 to 4 carbon atoms, an alkoxy group having 1 to 4 carbonatoms, and an alkoxycarbonyl group having 1 to 5 carbon atoms. Further,R² represents hydrogen or an alkyl group having 1 to 4 carbon atoms.Furthermore, R⁴ to R⁶ separately represent any of hydrogen, an alkylgroup having 1 to 4 carbon atoms, an alkoxy group having 1 to 4 carbonatoms, a halogen group, a trifluoromethyl group, and an aryl grouphaving 6 to 12 carbon atoms. Further, R⁷ and R⁸ separately represent analkyl group having 1 to 4 carbon atoms or an aryl group having 6 to 12carbon atoms. In addition, R⁷ and R⁸ may be bonded to each other througha carbon atom, an oxygen atom, a sulfur atom, or a nitrogen atom havinga substituent, to form a substituted or unsubstituted five-membered ringor a substituted or unsubstituted six-membered ring. Further, M is acentral metal and represents a Group 9 element or a Group 10 element.

An organometallic complex having the above structure is synthesized in adramatically high yield because generation of an impurity anddecomposition of the objective substance are suppressed in the synthesisreaction.

Another embodiment of the present invention is an organometallic complexwhich is represented by the following general formula (G3) and has astructure in which an m-aminophenyl pyrazine derivative is coordinatedto a Group 9 or Group 10 metal ion.

Note that in the general formula (G3), R¹ represents any of an alkylgroup having 1 to 4 carbon atoms, an alkoxy group having 1 to 4 carbonatoms, and an alkoxycarbonyl group having 1 to 5 carbon atoms. Further,R² represents hydrogen or an alkyl group having 1 to 4 carbon atoms.Furthermore, R⁴ and R⁵ separately represent any of hydrogen, an alkylgroup having 1 to 4 carbon atoms, an alkoxy group having 1 to 4 carbonatoms, a halogen group, a trifluoromethyl group, and an aryl grouphaving 6 to 12 carbon atoms. Further, R⁷ and R⁸ separately represent analkyl group having 1 to 4 carbon atoms or an aryl group having 6 to 12carbon atoms. In addition, R⁷ and R⁸ may be bonded to each other througha carbon atom, an oxygen atom, a sulfur atom, or a nitrogen atom havinga substituent, to form a substituted or unsubstituted five-membered ringor a substituted or unsubstituted six-membered ring. Further, M is acentral metal and represents a Group 9 element or a Group 10 element.

An organometallic complex having the above structure is preferablebecause the organometallic complex emits red phosphorescence and theligand is synthesized easily.

Another embodiment of the present invention is an organometallic complexhaving a structure represented by the following general formula (G4).

Note that in the general formula (G4), R¹ represents any of an alkylgroup having 1 to 4 carbon atoms, an alkoxy group having 1 to 4 carbonatoms, and an alkoxycarbonyl group having 1 to 5 carbon atoms. Further,R² and R³ separately represent hydrogen or an alkyl group having 1 to 4carbon atoms. Furthermore, R⁴ to R⁶ separately represent any ofhydrogen, an alkyl group having 1 to 4 carbon atoms, an alkoxy grouphaving 1 to 4 carbon atoms, a halogen group, a trifluoromethyl group,and an aryl group having 6 to 12 carbon atoms. Further, R⁷ and R⁸separately represent an alkyl group having 1 to 4 carbon atoms or anaryl group having 6 to 12 carbon atoms. In addition, R⁷ and R⁸ may bebonded to each other through a carbon atom, an oxygen atom, a sulfuratom, or a nitrogen atom having a substituent, to form a substituted orunsubstituted five-membered ring or a substituted or unsubstitutedsix-membered ring. Further, M is a central metal and represents a Group9 element or a Group 10 element. L represents a monoanionic ligand.Moreover, n is 2 when the central metal is a Group 9 element, and n is 1when the central metal is a Group 10 element.

The above organometallic complex is a specific example of theorganometallic complex which is represented by the following generalformula (G1) and has a structure in which an m-aminophenyl pyrazinederivative is coordinated to a Group 9 or Group 10 metal ion, and is acompound which emits red phosphorescence. In addition, theorganometallic complex has a low molecular weight, and high thermalstability and sublimation property, and thus can be easily evaporated infabrication of an element.

An organometallic complex of an m-aminophenyl pyrazine derivative inwhich an amino group is bonded at a meta position can emit red lightwith high color purity (as compared to an organometallic complex of anaminophenyl pyrazine derivative in which an amino group is bonded at anortho position or a para position). In addition, the organometalliccomplex of an m-aminophenyl pyrazine derivative in which an amino groupis bonded at a meta position has a reduced steric hindrance in themolecule and high stability of the molecule, and thus reliability of theelement is increased (as compared to the organometallic complex of anaminophenyl pyrazine derivative in which an amino group is bonded at anortho position or a para position).

Another embodiment of the present invention is an organometallic complexhaving a structure represented by the following general formula (G5).

Note that in the general formula (G5), R¹ represents any of an alkylgroup having 1 to 4 carbon atoms, an alkoxy group having 1 to 4 carbonatoms, and an alkoxycarbonyl group having 1 to 5 carbon atoms. Further,R² represents hydrogen or an alkyl group having 1 to 4 carbon atoms.Furthermore, R⁴ to R⁶ separately represent any of hydrogen, an alkylgroup having 1 to 4 carbon atoms, an alkoxy group having 1 to 4 carbonatoms, a halogen group, a trifluoromethyl group, and an aryl grouphaving 6 to 12 carbon atoms. Further, R⁷ and R⁸ separately represent analkyl group having 1 to 4 carbon atoms or an aryl group having 6 to 12carbon atoms. In addition, R⁷ and R⁸ may be bonded to each other througha carbon atom, an oxygen atom, a sulfur atom, or a nitrogen atom havinga substituent, to form a substituted or unsubstituted five-membered ringor a substituted or unsubstituted six-membered ring. Further, M is acentral metal and represents a Group 9 element or a Group 10 element. Lrepresents a monoanionic ligand. Moreover, n is 2 when the central metalis a Group 9 element, and n is 1 when the central metal is a Group 10element.

The above organometallic complex is a specific example of theorganometallic complex which is represented by the general formula (G2)and has a structure in which an m-aminophenyl pyrazine derivative iscoordinated to a Group 9 or Group 10 metal ion. The organometalliccomplex emits red phosphorescence and the ligand is synthesized easily.In addition, the yield is dramatically increased because generation ofan impurity and decomposition of the objective substance are suppressedin the synthesis reaction.

Another embodiment of the present invention is an organometallic complexhaving a structure represented by the following general formula (G6).

Note that in the general formula (G6), R¹ represents any of an alkylgroup having 1 to 4 carbon atoms, an alkoxy group having 1 to 4 carbonatoms, and an alkoxycarbonyl group having 1 to 5 carbon atoms. Further,R² represents hydrogen or an alkyl group having 1 to 4 carbon atoms.Furthermore, R⁴ and R⁵ separately represent any of hydrogen, an alkylgroup having 1 to 4 carbon atoms, an alkoxy group having 1 to 4 carbonatoms, a halogen group, a trifluoromethyl group, and an aryl grouphaving 6 to 12 carbon atoms. Further, R⁷ and R⁸ separately represent analkyl group having 1 to 4 carbon atoms or an aryl group having 6 to 12carbon atoms. In addition, R⁷ and R⁸ may be bonded to each other througha carbon atom, an oxygen atom, a sulfur atom, or a nitrogen atom havinga substituent, to form a substituted or unsubstituted five-membered ringor a substituted or unsubstituted six-membered ring. Further, M is acentral metal and represents a Group 9 element or a Group 10 element. Lrepresents a monoanionic ligand. Moreover, n is 2 when the central metalis a Group 9 element, and n is 1 when the central metal is a Group 10element.

The above organometallic complex is a specific example of theorganometallic complex which is represented by the general formula (G3)and has a structure in which an m-aminophenyl pyrazine derivative iscoordinated to a Group 9 or Group 10 metal ion. The organometalliccomplex is preferable because the organometallic complex emits redphosphorescence and the ligand is synthesized easily.

Another embodiment of the present invention is an organometallic complexin which the monoanionic ligand according to the general formula (G4),the general formula (G5), or the general formula (G6) is any of thefollowing: a monoanionic bidentate chelate ligand having a β-diketonestructure, a monoanionic bidentate chelate ligand having a carboxylgroup, a monoanionic bidentate chelate ligand having a phenolic hydroxylgroup, and a monoanionic bidentate chelate ligand in which two ligandelements are both nitrogen.

The above organometallic complex is a specific example of theorganometallic complex which is represented by the general formula (G4),the general formula (G5), or the general formula (G6), and is a compoundwhich emits red phosphorescence. In addition, the organometallic complexhas a low molecular weight, and high thermal stability and sublimationproperty, and thus can be easily evaporated in fabrication of anelement.

An organometallic complex of an m-aminophenyl pyrazine derivative inwhich an amino group is bonded at a meta position can emit red lightwith high color purity as compared to an organometallic complex of anaminophenyl pyrazine derivative in which an amino group is bonded at anortho position or a para position. In addition, the organometalliccomplex of an m-aminophenyl pyrazine derivative in which an amino groupis bonded at a meta position has a reduced steric hindrance in themolecule and high stability of the molecule, and thus reliability of theelement is increased as compared to the organometallic complex of anaminophenyl pyrazine derivative in which an amino group is bonded at anortho position or a para position.

Another embodiment of the present invention is an organometallic complexin which the monoanionic ligand according to the general formula (G4),the general formula (G5), or the general formula (G6) includes any ofthe following structural formulas (L1) to (L8).

Any of the ligands has high coordinative ability and can be obtained ata low cost. Therefore, the organometallic complex is stable, and theorganometallic complex can be provided at a low cost.

Another embodiment of the present invention is an organometallic complexhaving a structure represented by the following general formula (G7).

Note that in the general formula (G7), R¹ represents any of an alkylgroup having 1 to 4 carbon atoms, an alkoxy group having 1 to 4 carbonatoms, and an alkoxycarbonyl group having 1 to 5 carbon atoms. Further,R² and R³ separately represent hydrogen or an alkyl group having 1 to 4carbon atoms. Furthermore, R⁴ to R⁶ separately represent any ofhydrogen, an alkyl group having 1 to 4 carbon atoms, an alkoxy grouphaving 1 to 4 carbon atoms, a halogen group, a trifluoromethyl group,and an aryl group having 6 to 12 carbon atoms. Further, R⁷ and R⁸separately represent an alkyl group having 1 to 4 carbon atoms or anaryl group having 6 to 12 carbon atoms. In addition, R⁷ and R⁸ may bebonded to each other through a carbon atom, an oxygen atom, a sulfuratom, or a nitrogen atom having a substituent, to form a substituted orunsubstituted five-membered ring or a substituted or unsubstitutedsix-membered ring. Further, M is a central metal and represents a Group9 element or a Group 10 element. Moreover, n is 2 when the central metalis a Group 9 element, and n is 1 when the central metal is a Group 10element.

An organometallic complex having the structure represented by thegeneral formula (G7) is an organometallic complex in which only the samem-aminophenyl pyrazine derivatives are coordinated to a Group 9 or Group10 metal ion in the organometallic complex represented by the generalformula (G4). Such a structure is preferable for higher heat resistanceand higher reliability of the element.

Another embodiment of the present invention is an organometallic complexhaving a structure represented by the following general formula (G8).

Note that in the general formula (G8), R¹ represents any of an alkylgroup having 1 to 4 carbon atoms, an alkoxy group having 1 to 4 carbonatoms, and an alkoxycarbonyl group having 1 to 5 carbon atoms. Further,R² represents hydrogen or an alkyl group having 1 to 4 carbon atoms.Furthermore, R⁴ to R⁶ separately represent any of hydrogen, an alkylgroup having 1 to 4 carbon atoms, an alkoxy group having 1 to 4 carbonatoms, a halogen group, a trifluoromethyl group, and an aryl grouphaving 6 to 12 carbon atoms. Further, R⁷ and R⁸ separately represent analkyl group having 1 to 4 carbon atoms or an aryl group having 6 to 12carbon atoms. In addition, R⁷ and R⁸ may be bonded to each other througha carbon atom, an oxygen atom, a sulfur atom, or a nitrogen atom havinga substituent, to form a substituted or unsubstituted five-membered ringor a substituted or unsubstituted six-membered ring. Further, M is acentral metal and represents a Group 9 element or a Group 10 element.Moreover, n is 2 when the central metal is a Group 9 element, and n is 1when the central metal is a Group 10 element.

An organometallic complex having the structure represented by thegeneral formula (G8) is an organometallic complex in which only the samem-aminophenyl pyrazine derivatives are coordinated to a Group 9 or Group10 metal ion in the organometallic complex represented by the generalformula (G5). Such a structure is preferable because generation of animpurity and decomposition of the objective substance are suppressed inthe synthesis reaction; and thus the synthesis yield is dramaticallyincreased.

Another embodiment of the present invention is an organometallic complexhaving a structure represented by the following general formula (G9).

Note that in the general formula (G9), R¹ represents any of an alkylgroup having 1 to 4 carbon atoms, an alkoxy group having 1 to 4 carbonatoms, and an alkoxycarbonyl group having 1 to 5 carbon atoms. Further,R² represents hydrogen or an alkyl group having 1 to 4 carbon atoms.Furthermore, R⁴ and R⁵ separately represent any of hydrogen, an alkylgroup having 1 to 4 carbon atoms, an alkoxy group having 1 to 4 carbonatoms, a halogen group, a trifluoromethyl group, and an aryl grouphaving 6 to 12 carbon atoms. Further, R⁷ and R⁸ separately represent analkyl group having 1 to 4 carbon atoms or an aryl group having 6 to 12carbon atoms. In addition, R⁷ and R⁸ may be bonded to each other througha carbon atom, an oxygen atom, a sulfur atom, or a nitrogen atom havinga substituent, to form a substituted or unsubstituted five-membered ringor a substituted or unsubstituted six-membered ring. Further, M is acentral metal and represents a Group 9 element or a Group 10 element.Moreover, n is 2 when the central metal is a Group 9 element, and n is 1when the central metal is a Group 10 element.

An organometallic complex having the structure represented by thegeneral formula (G9) is an organometallic complex in which only the samem-aminophenyl pyrazine derivatives are coordinated to a Group 9 or Group10 metal ion in the organometallic complex represented by the generalformula (G6). Such a structure is preferable because the organometalliccomplex emits red phosphorescence and the ligand is synthesized easily.

Another embodiment of the present invention is an organometallic complexin which the central metal M is iridium or platinum in any of theabove-described organometallic complexes.

The above organometallic complex including iridium or platinum as thecentral metal M emits phosphorescence efficiently. This is becauseiridium or platinum provides a prominent heavy atom effect.

Another embodiment of the present invention is a light-emitting elementincluding any of the above organometallic complexes. The organometalliccomplex can convert triplet excitation energy into red light emission.Therefore, the organometallic complex has an effect of increasing theemission efficiency of the light-emitting element.

Another embodiment of the present invention is a light-emitting elementincluding any of the above organometallic complexes as a light-emittingsubstance. Since the organometallic complex emits phosphorescence, theuse of the organometallic complex as a light-emitting substance has aneffect of increasing the efficiency of the light-emitting element.

Another embodiment of the present invention is a light-emitting deviceincluding any of the above light-emitting elements. Application of thehigh-efficiency light-emitting element including the fluorescentorganometallic complex can reduce the power consumption of thelight-emitting device.

One embodiment of the present invention includes, in its category, anelectronic device including the light-emitting device. Application ofthe high-efficiency light-emitting device including the phosphorescentorganometallic complex can reduce the power consumption of theelectronic device.

Note that the light-emitting device in this specification refers to animage display device, a light-emitting device, or a light source(including a lighting device). Further, the light-emitting deviceincludes any of the following modules in its category: a module in whicha connector such as a flexible printed circuit (FPC), a tape automatedbonding (TAB) tape, or a tape carrier package (TCP) is attached to alight-emitting device; a module having a TAB tape or a TCP provided witha printed wiring board at the end thereof; and a module having anintegrated circuit (IC) directly mounted over a light-emitting device bya chip on glass (COG) method.

One embodiment of the present invention provides a novel phosphorescentorganometallic complex.

Another embodiment of the present invention provides an organometalliccomplex which emits red phosphorescence.

Another embodiment of the present invention provides a light-emittingelement which emits red phosphorescence.

Another embodiment of the present invention provides a light-emittingdevice.

Another embodiment of the present invention provides an electronicdevice.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a view illustrating a light-emitting element according to oneembodiment of the present invention.

FIG. 2 is a view illustrating a light-emitting element according to oneembodiment of the present invention.

FIG. 3 is a view illustrating a light-emitting element according to oneembodiment of the present invention.

FIGS. 4A to 4D are views illustrating a passive matrix light-emittingdevice.

FIG. 5 is a view illustrating a passive matrix light-emitting device.

FIGS. 6A and 6B are views illustrating an active matrix light-emittingdevice.

FIGS. 7A to 7E are views illustrating electronic devices.

FIG. 8 is a view illustrating lighting devices.

FIG. 9 shows a ¹H-NMR chart of an organometallic complex represented bya structural formula (100).

FIG. 10 shows an ultraviolet-visible absorption spectrum and an emissionspectrum of the organometallic complex represented by the structuralformula (100).

FIG. 11 shows a ¹H-NMR chart of [Ir(dmdpappr)₂(acac)] synthesized inComparative Example.

FIG. 12 shows an ultraviolet-visible absorption spectrum and an emissionspectrum of [Ir(dmdpappr)₂(acac)] synthesized in Comparative Example.

DETAILED DESCRIPTION OF THE INVENTION

Hereinafter, Embodiments of the present invention will be described indetail with reference to the drawings. However, the present invention isnot limited to the following description, and the mode and details canbe variously changed unless departing from the scope and spirit of theinvention. Therefore, the invention should not be construed as beinglimited to the description in the following embodiments.

Embodiment 1

Embodiment 1 shows organometallic complexes which are embodiments of thepresent invention and methods for synthesis thereof. Specifically,description is given of methods of synthesizing an m-aminophenylpyrazine derivative and an organometallic complex having a structure inwhich the m-aminophenyl pyrazine derivative is coordinated to a Group 9or Group 10 metal ion.

[Method of Synthesizing m-Aminophenyl Pyrazine Derivative Represented byGeneral Formula (G0)]

The m-aminophenyl pyrazine derivative represented by the followinggeneral formula (G0) can be synthesized by any of the following simplesynthesis schemes (a), (a′), and (a″). Note that in each of thesynthesis schemes (a), (a′), and (a″), X represents a halogen.

In the general formula (G0), R¹ represents any of an alkyl group having1 to 4 carbon atoms, an alkoxy group having 1 to 4 carbon atoms, and analkoxycarbonyl group having 1 to 5 carbon atoms. Further, R² and R³separately represent hydrogen or an alkyl group having 1 to 4 carbonatoms. Furthermore, R⁴ to R⁶ separately represent any of hydrogen, analkyl group having 1 to 4 carbon atoms, an alkoxy group having 1 to 4carbon atoms, a halogen group, a trifluoromethyl group, and an arylgroup having 6 to 12 carbon atoms. Further, R⁷ and R⁸ separatelyrepresent an alkyl group having 1 to 4 carbon atoms or an aryl grouphaving 6 to 12 carbon atoms. In addition, R⁷ and R⁸ may be bonded toeach other through a carbon atom, an oxygen atom, a sulfur atom, or anitrogen atom having a substituent, to form a substituted orunsubstituted five-membered ring or a substituted or unsubstitutedsix-membered ring.

As shown in the following scheme (a) for example, the m-aminophenylpyrazine derivative can be obtained by a reaction between a lithiumcompound of m-alkoxyaryl or a Grignard reagent of m-alkoxyaryl shown as(A1) and a pyrazine compound (A2).

Alternatively, as shown in the following scheme (a′), the m-aminophenylpyrazine derivative can be obtained by coupling of m-alkoxyphenylboronic acid (A1′) and a halogenated pyrazine compound (A2′).

Further alternatively, as shown in the following scheme (a″), them-aminophenyl pyrazine derivative can be obtained by a reaction betweendiketone of m-alkoxyaryl (A1″) and diamine (A2″).

Various types of the above-described compounds (A1), (A2), (A1′), (A2′),(A1″), and (A2″) are commercially available or can be synthesized.Accordingly, it is possible to synthesize many types of them-alkoxyphenyl pyrazine derivative represented by the general formula(G0). Therefore, features of the organometallic complex according to oneembodiment of the present invention include a wide variety of ligandsthereof, effects of emitting phosphorescence, and potential contributionto various light-emitting properties.

[Method of Synthesizing Organometallic Complex, One Embodiment of thePresent Invention Represented by General Formula (G4)]

Next, description is given of methods of synthesizing an organometalliccomplex which is formed by orthometalation of an m-aminophenyl pyrazinederivative represented by the general formula (G0), i.e., anorganometallic complex represented by the following general formula(G1). Specifically, the description includes a method of synthesizing anorganometallic complex represented by the following general formula (G4)and a method of synthesizing an organometallic complex represented bythe following general formula (G7).

In the general formulas (G1), (G4), and (G7), R¹ represents any of analkyl group having 1 to 4 carbon atoms, an alkoxy group having 1 to 4carbon atoms, and an alkoxycarbonyl group having 1 to 5 carbon atoms.Further, R² and R³ separately represent hydrogen or an alkyl grouphaving 1 to 4 carbon atoms. Furthermore, R⁴ to R⁶ separately representany of hydrogen, an alkyl group having 1 to 4 carbon atoms, an alkoxygroup having 1 to 4 carbon atoms, a halogen group, a trifluoromethylgroup, and an aryl group having 6 to 12 carbon atoms. Further, R⁷ and R⁸separately represent an alkyl group having 1 to 4 carbon atoms or anaryl group having 6 to 12 carbon atoms. In addition, R⁷ and R⁸ may bebonded to each other through a carbon atom, an oxygen atom, a sulfuratom, or a nitrogen atom having a substituent, to form a substituted orunsubstituted five-membered ring or a substituted or unsubstitutedsix-membered ring. Further, M is a central metal and represents a Group9 element or a Group 10 element. In the general formulas (G4) and (G7),n is 2 when the central metal is a Group 9 element, and n is 1 when thecentral metal is a Group 10 element. In the general formula (G4), Lrepresents a monoanionic ligand.

First, as shown in the following synthesis scheme (b), the m-aminophenylpyrazine derivative represented by the general formula (G0) and acompound of a metal belonging to Group 9 or Group 10 which contains ahalogen (a metal halide or a metal complex) are heated with analcohol-based solvent (e.g., glycerol, ethyleneglycol, 2-methoxyethanol,or 2-ethoxyethanol) alone or with a mixed solvent of water and one ormore kinds of the above alcohol-based solvents, thereby obtaining abinuclear complex (B), which is a type of organometallic complexeshaving the structure represented by the general formula (G1).

Examples of the Group 9 or Group 10 metal compound containing a halogeninclude rhodium chloride hydrate, palladium chloride, iridium chloridehydrate, iridium chloride hydrochloride hydrate, potassiumtetrachloroplatinate(II), and the like, but are not limited to theseexamples. Note that in the synthesis scheme (b), M represents a Group 9element or a Group 10 element, and X represents a halogen. Moreover, nis 2 when M is a Group 9 element, and n is 1 when M is a Group 10element.

Next, the binuclear organometallic complex (B) is reacted with amaterial HL of a monoanionic ligand, thereby obtaining theorganometallic complex represented by the general formula (G4)(synthesis scheme (c)). Note that in the synthesis scheme (c), Mrepresents a Group 9 element or a Group 10 element, and X represents ahalogen. Moreover, n is 2 when M is a Group 9 element, and n is 1 when Mis a Group 10 element.

Examples of the monoanionic ligand (L) in the general formula (G4)include a monoanionic bidentate chelate ligand having a b-diketonestructure, a monoanionic bidentate chelate ligand having a carboxylgroup, a monoanionic bidentate chelate ligand having a phenolic hydroxylgroup, or a monoanionic bidentate chelate ligand in which two ligandelements are both nitrogen.

Further, the monoanionic ligand (L) in the general formula (G4) can beany of the following structural formulas (L1) to (L8).

The organometallic complex represented by the above general formula (G7)can be synthesized by the following synthesis scheme (d). In otherwords, the organometallic complex represented by the general formula(G7) can be obtained by heating the organometallic complex representedby the general formula (G4) and the m-aminophenyl pyrazine derivativerepresented by the general formula (G0) in a high boiling solvent suchas glycerin at a high temperature of about 200° C. Note that in thesynthesis scheme (d), M represents a Group 9 element or a Group 10element, and X represents a halogen. Moreover, n is 2 when M is a Group9 element, and n is 1 when M is a Group 10 element.

Examples of the synthesis methods are described above, but methods ofsynthesizing the organometallic complex according to one embodiment ofthe present invention are not limited thereto.

The organometallic complex according to one embodiment of the presentinvention can be combined with any of a variety of central metals M andmonoanionic ligands L as appropriate to form a variety of organometalliccomplexes. Specifically, the organometallic complex according to oneembodiment of the present invention is represented by any of thefollowing structural formulas (the following structural formulas (100)to (147)). Note that the present invention is not limited to thesestructural formulas.

Note that there can be geometrical isomers and stereoisomers of theorganometallic complexes represented by the structural formulas (100) to(147) depending on the type of ligand. The organometallic complexaccording to one embodiment of the present invention includes all ofthese isomers.

The above-described organometallic complexes according to embodiments ofthe present invention can be used as photosensitizers owing to thecapability of intersystem crossing. Further, the organometalliccomplexes can be used as light-emitting materials or light-emittingsubstances in light-emitting elements owing to the capability ofphosphorescence.

Embodiment 2

This embodiment shows a mode of a light-emitting element in which theorganometallic complex according to one embodiment of the presentinvention is used for a light-emitting layer, with reference to FIG. 1.

FIG. 1 illustrates a light-emitting element having an EL layer 102between a first electrode 101 and a second electrode 103. Thelight-emitting layer 113 contains any of the organometallic complexeswhich are embodiments of the present invention. This embodiment shows acase where the first electrode 101 serves as an anode and the secondelectrode 103 serves as a cathode.

When a voltage is applied between the first electrode 101 and the secondelectrode 103 of the light-emitting element illustrated in FIG. 1 sothat a potential of the first electrode 101 is higher than that of thesecond electrode 103, holes are injected from the first electrode 101side, and electrons are injected from the second electrode 103 side tothe EL layer 102. Holes and electrons injected to the EL layer 102recombine in the light-emitting layer 113 to produce an excited state ofthe organometallic complex according to one embodiment of the presentinvention. When the organometallic complex in the excited state relaxesto the ground state, light is emitted. Thus, the organometallic complexaccording to one embodiment of the present invention functions as alight-emitting substance in the light-emitting element.

In order to be used as an anode, the first electrode 101 is preferablyformed using a metal, an alloy, an electrically conductive compound, amixture thereof, or the like having a high work function (specifically,greater than or equal to 4.0 eV). Specific examples include a mixedoxide of indium oxide and tin oxide, a mixed oxide of indium oxide andzinc oxide, a mixed oxide of indium oxide and tin oxide containingsilicon or silicon oxide, a mixed oxide of indium oxide and zinc oxidecontaining silicon or silicon oxide, gold (Au), platinum (Pt), nickel(Ni), tungsten (W), chromium (Cr), molybdenum (Mo), iron (Fe), cobalt(Co), copper (Cu), palladium (Pd), nitride of a metal material (forexample, titanium nitride), and the like.

When a layer included in the EL layer 102 and formed in contact with thefirst electrode 101 is formed using a later-described composite materialin which an organic compound and an electron acceptor (acceptor) aremixed, the first electrode 101 can be formed using any of a variety ofmetals, alloys, and electrically conductive compounds, a mixturethereof, and the like regardless of the work function. For example,aluminum (Al), silver (Ag), an alloy containing aluminum (e.g., AlSi),or the like can also be used.

The first electrode 101 can be formed by, for example, a sputteringmethod, an evaporation method (including a vacuum evaporation method),or the like.

The EL layer 102 formed over the first electrode 101 may include atleast the light-emitting layer 113 containing the organometallic complexaccording to one embodiment of the present invention. For part of the ELlayer 102, a known substance can be used, and either a low molecularcompound or a high molecular compound can be used.

As illustrated in FIG. 1, the EL layer 102 is formed by stacking, inaddition to the light-emitting layer 113, a hole-injection layer 111containing a substance having a high hole-injection property, ahole-transport layer 112 containing a substance having a highhole-transport property, an electron-transport layer 114 containing asubstance having a high electron-transport property, anelectron-injection layer 115 containing a substance having a highelectron-injection property, and the like, as appropriate.

The hole-injection layer 111 contains a substance having a highhole-injection property. As the substance having a high hole-injectionproperty, a metal oxide can be used, such as molybdenum oxide, titaniumoxide, vanadium oxide, rhenium oxide, ruthenium oxide, chromium oxide,zirconium oxide, hafnium oxide, tantalum oxide, silver oxide, tungstenoxide, or manganese oxide. Alternatively, a phthalocyanine compound canbe used, such as phthalocyanine (abbreviation: H₂Pc), copper(II)phthalocyanine (abbreviation: CuPc), or vanadyl phthalocyanine(abbreviation: VOPc).

Alternatively, an aromatic amine compound which is a low molecularorganic compound can be used, such as4,4′,4″-tris(N,N-diphenylamino)triphenylamine (abbreviation: TDATA),4,4′,4″-tris[N-(3-methylphenyl)-N-phenylamino]triphenylamine(abbreviation: MTDATA),4,4′-bis[N-(4-diphenylaminophenyl)-N-phenylamino]biphenyl (abbreviation:DPAB),4,4′-bis(N-{4-[N′-(3-methylphenyl)-N′-phenylamino]phenyl}-N-phenylamino)biphenyl(abbreviation: DNTPD),1,3,5-tris[N-(4-diphenylaminophenyl)-N-phenylamino]benzene(abbreviation: DPA3B),3-[N-(9-phenylcarbazol-3-yl)-N-phenylamino]-9-phenylcarbazole(abbreviation: PCzPCA1),3,6-bis[N-(9-phenylcarbazol-3-yl)-N-phenylamino]-9-phenylcarbazole(abbreviation: PCzPCA2), or3-[N-(1-naphthyl)-N-(9-phenylcarbazol-3-yl)amino]-9-phenylcarbazole(abbreviation: PCzPCN1).

Alternatively, a high molecular compound can be used, such aspoly(N-vinylcarbazole) (abbreviation: PVK), poly(4-vinyltriphenylamine)(abbreviation: PVTPA),poly[N-(4-{N′-[4-(4-diphenylamino)phenyl]phenyl-N′-phenylamino}phenyl)methacrylamide](abbreviation: PTPDMA), orpoly[N,N′-bis(4-butylphenyl)-N,N′-bis(phenyl)benzidine] (abbreviation:Poly-TPD). Alternatively, a high molecular compound to which acid isadded can be used, such aspoly(3,4-ethylenedioxythiophene)/poly(styrenesulfonic acid) (PEDOT/PSS),or polyaniline/poly(styrenesulfonic acid) (PAni/PSS).

Alternatively, the hole-injection layer 111 may be formed using acomposite material containing an organic compound and an electronacceptor (acceptor). Such a composite material is superior in ahole-injection property and a hole-transport property, since holes aregenerated in the organic compound by the electron acceptor. In thiscase, the organic compound is preferably a material excellent intransporting the generated holes (a substance having a highhole-transport property).

Examples of an organic compound that can be used for the compositematerial include various compounds; for example, it is possible to use alow molecular compound such as an aromatic amine compound, a carbazolederivative, an aromatic hydrocarbon compound, or a compound in which thebasic skeleton is any of the low molecular compounds, such as oligomer,dendrimer, or polymer. The organic compound used for the compositematerial is preferably an organic compound having a high hole-transportproperty. Specifically, a substance having a hole mobility of 10⁻⁶cm²/V·s or higher is preferably used. However, another substance mayalso be used as long as the substance has a higher hole-transportproperty than an electron-transport property. The organic compoundswhich can be used for the composite material are specifically shownbelow.

Examples of the organic compound that can be used for the compositematerial include aromatic amine compounds such as TDATA, MTDATA, DPAB,DNTPD, DPA3B, PCzPCA1, PCzPCA2, PCzPCN1,4,4′-bis[N-(1-naphthyl)-N-phenylamino]biphenyl (abbreviation: NPB), andN,N′-bis(3-methylphenyl)-N,N′-diphenyl-[1,1′-biphenyl]-4,4′-diamine(abbreviation: TPD), and carbazole derivatives such as4,4′-di(N-carbazolyl)biphenyl (abbreviation: CBP),1,3,5-tris[4-(N-carbazolyl)phenyl]benzene (abbreviation: TCPB),9-[4-(N-carbazolyl)phenyl]-10-phenylanthracene (abbreviation: CzPA), and1,4-bis[4-(N-carbazolyl)phenyl-2,3,5,6-tetraphenylbenzene.

Examples of the aromatic hydrocarbon compound include2-tert-butyl-9,10-di(2-naphthyl)anthracene (abbreviation: t-BuDNA),2-tert-butyl-9,10-di(1-naphthyl)anthracene,9,10-bis(3,5-diphenylphenyl)anthracene (abbreviation: DPPA),2-tert-butyl-9,10-bis(4-phenylphenyl)anthracene (abbreviation: t-BuDBA),9,10-di(2-naphthyl)anthracene (abbreviation: DNA),9,10-diphenylanthracene (abbreviation: DPAnth), 2-tert-butylanthracene(abbreviation: t-BuAnth), 9,10-bis(4-methyl-1-naphthyl)anthracene(abbreviation: DMNA),9,10-bis[2-(1-naphthyl)phenyl]-2-tert-butylanthracene,9,10-bis[2-(1-naphthyl)phenyl]anthracene,2,3,6,7-tetramethyl-9,10-di(1-naphthyl)anthracene, and the like.

Examples of the aromatic hydrocarbon compound further include2,3,6,7-tetramethyl-9,10-di(2-naphthyl)anthracene, 9,9′-bianthryl,10,10′-diphenyl-9,9′-bianthryl,10,10′-bis(2-phenylphenyl)-9,9′-bianthryl,10,10′-bis[(2,3,4,5,6-pentaphenyl)phenyl]-9,9′-bianthryl, anthracene,tetracene, rubrene, perylene, 2,5,8,11-tetra(tert-butyl)perylene,pentacene, coronene, 4,4′-bis(2,2-diphenylvinyl)biphenyl (abbreviation:DPVBi), 9,10-bis[4-(2,2-diphenylvinyl)phenyl]anthracene (abbreviation:DPVPA), and the like.

As the electron acceptor, it is possible to use an organic compound suchas 7,7,8,8-tetracyano-2,3,5,6-tetrafluoroquinodimethane (abbreviation:F₄-TCNQ) or chloranil, or a transition metal oxide. Alternatively, it ispossible to use an oxide of a metal belonging to any of Groups 4 to 8 inthe periodic table. Specifically, the following oxides are preferablebecause their electron-accepting property is high: vanadium oxide,niobium oxide, tantalum oxide, chromium oxide, molybdenum oxide,tungsten oxide, manganese oxide, and rhenium oxide. Among these,molybdenum oxide is especially preferable because it is stable in theair and its hygroscopic property is low and is easily treated.

Note that the hole-injection layer 111 may be formed using a compositematerial of any of the above-described high molecular compounds, such asPVK, PVTPA, PTPDMA, or Poly-TPD, and any of the above-described electronacceptors.

The hole-transport layer 112 contains a substance having a highhole-transport property. As the substance having a high hole-transportproperty, an aromatic amine compound can be used, such as NPB, TPD,4,4′-bis[N-(9,9-dimethylfluoren-2-yl)-N-phenylamino]biphenyl(abbreviation: DFLDPBi), or4,4′-bis[N-(spiro-9,9′-bifluoren-2-yl)-N-phenylamino]biphenyl(abbreviation: BSPB). The substances mentioned here are mainly ones thathave a hole mobility of 10⁻⁶ cm²V·s or higher. However, anothersubstance may also be used as long as the substance has a higherhole-transport property than an electron-transport property. The layercontaining a substance having a high hole-transport property is notlimited to a single layer, and two or more layers containing theaforementioned substances may be stacked.

Alternatively, the hole-transport layer 112 can be formed using a highmolecular compound such as PVK, PVTPA, PTPDMA, or Poly-TPD.

In the light-emitting layer 113, the organometallic complex according toone embodiment of the present invention is dispersed in an organic layer(a so-called host layer). The dispersed organometallic complex canprevent concentration quenching. The host layer is formed using asubstance whose triplet excitation energy is higher than that of theorganometallic complex. Therefore, the organometallic complex can emitlight efficiently. Note that the triplet excitation energy indicates anenergy difference between a ground state and a triplet excited state.

The material contained in the host layer used for dispersing theorganometallic complex is preferably, but not limited to, any ofcompounds having an arylamine skeleton, such as2,3-bis(4-diphenylaminophenyl)quinoxaline (abbreviation: TPAQn) and NPB,carbazole derivatives such as CBP and4,4′,4″-tris(N-carbazolyl)triphenylamine (abbreviation: TCTA), and metalcomplexes such as bis[2-(2-hydroxyphenyl)pyridinato]zinc (abbreviation:Znpp₂), bis[2-(2-hydroxyphenyl)benzoxazolato]zinc (abbreviation:Zn(BOX)₂), bis(2-methyl-8-quinolinolato)(4-phenylphenolato)aluminum(abbreviation: BAlq), and tris(8-quinolinolato)aluminum (abbreviation:Alq₃). Alternatively, a high molecular compound such as PVK can be used.

The electron-transport layer 114 contains a substance having a highelectron-transport property. The electron-transport layer 114 can beformed using a metal complex such as Alq₃,tris(4-methyl-8-quinolinolato)aluminum (abbreviation: Almq₃),bis(10-hydroxybenzo[h]quinolinato)beryllium (abbreviation: BeBq₂), BAlq,Zn(BOX)₂, or bis[2-(2-hydroxyphenyl)benzothiazolato]zinc (abbreviation:Zn(BTZ)₂). In addition, it is possible to use a heteroaromatic compoundsuch as 2-(4-biphenylyl)-5-(4-tert-butylphenyl)-1,3,4-oxadiazole(abbreviation: PBD),1,3-bis[5-(p-tert-butylphenyl)-1,3,4-oxadiazol-2-yl]benzene(abbreviation: OXD-7),3-(4-tert-butylphenyl)-4-phenyl-5-(4-biphenylyl)-1,2,4-triazole(abbreviation: TAZ),3-(4-tert-butylphenyl)-4-(4-ethylphenyl)-5-(4-biphenylyl)-1,2,4-triazole(abbreviation: p-EtTAZ), bathophenanthroline (abbreviation: BPhen),bathocuproine (abbreviation: BCP), or4,4′-bis(5-methylbenzoxazol-2-yl)stilbene (abbreviation: BzOs). Further,it is possible to use a high molecular compound such aspoly(2,5-pyridinediyl) (abbreviation: PPy),poly[(9,9-dihexylfluorene-2,7-diyl)-co-(pyridine-3,5-diyl)](abbreviation: PPy) orpoly[(9,9-dioctylfluorene-2,7-diyl)-co-(2,2′-bipyridine-6,6′-diyl)](abbreviation: PF-BPy). The substances mentioned here are mainly onesthat have an electron mobility of 10⁻⁶ cm²V·s or higher. Note that anysubstance other than the above substances may be used for theelectron-transport layer as long as the substance has a higherelectron-transport property than a hole-transport property.

The electron-transport layer is not limited to a single layer, and twoor more layers formed using the above substances may be stacked.

The electron-injection layer 115 contains a substance having a highelectron-injection property. The electron-injection layer 115 can beformed using a fluoride or oxide of an alkali metal or an alkaline earthmetal, such as lithium fluoride (LiF), cesium fluoride (CsF), calciumfluoride (CaF₂), or lithium oxide (LiO_(x)). Alternatively, a rare earthmetal compound can be used, such as erbium fluoride (ErF₃). Furtheralternatively, it is possible to use the above substances for formingthe electron-transport layer 114.

Alternatively, the electron-injection layer 115 may be formed using acomposite material in which an organic compound and an electron donor(donor) are mixed. The composite material is superior in anelectron-injection property and an electron-transport property, sinceelectrons are generated in the organic compound by the electron donor.In this case, the organic compound is preferably a material excellent intransporting the generated electrons; specifically, it is possible touse the above substances for forming the electron-transport layer 114(e.g., a metal complex or a heteroaromatic compound). As the electrondonor, a substance exhibiting an electron-donating property to theorganic compound may be used; specifically, it is preferable to use analkali metal, an alkaline-earth metal, or a rare earth metal, such aslithium, cesium, magnesium, calcium, erbium, or ytterbium. Further, analkali metal oxide or an alkaline-earth metal oxide is preferable, suchas lithium oxide, calcium oxide, or barium oxide. Alternatively, Lewisbase such as magnesium oxide can be used. Further alternatively, anorganic compound such as tetrathiafulvalene (abbreviation: TTF) can beused.

Note that each of the above-described hole-injection layer 111,hole-transport layer 112, light-emitting layer 113, electron-transportlayer 114, and electron-injection layer 115 can be formed by anevaporation method (including a vacuum evaporation method), an inkjetmethod, a coating method, or the like.

The second electrode 103 serves as a cathode. The cathode can be formedusing a metal, an alloy, an electrically conductive compound, a mixturethereof, or the like which has a low work function (specifically, 3.8 eVor less). Specific examples include elements that belong to Group 1 orGroup 2 of the periodic table, that is, alkali metals such as lithium(Li) and cesium (Cs) or alkaline earth metals such as magnesium (Mg),calcium (Ca), and strontium (Sr), or alloys thereof (e.g., MgAg andAlLi); rare earth metals such as europium (Eu) and ytterbium (Yb), oralloys thereof; aluminum (Al); silver (Ag); and the like.

The second electrode 103 can also be formed using aluminum, silver, amixed oxide of indium oxide and tin oxide, a mixed oxide of indium oxideand zinc oxide, a mixed oxide of indium oxide and tin oxide containingsilicon or silicon oxide, a mixed oxide of indium oxide and zinc oxidecontaining silicon or silicon oxide regardless of the work function. Inthis case, a layer included in the EL layer 102 and formed in contactwith the second electrode 103 is formed using the above-describedcomposite material in which an organic compound and an electron donor(donor) are mixed.

Note that the second electrode 103 can be formed by a vacuum evaporationmethod or a sputtering method. Alternatively, in the case of using asilver paste or the like, a coating method, an inkjet method, or thelike can be used.

In the above-described light-emitting element, current flows due to apotential difference generated between the first electrode 101 and thesecond electrode 103, and holes and electrons recombine in the EL layer102, whereby light is emitted. Then, this emitted light is extractedthrough either of the first electrode 101 or the second electrode 103,or both. For that purpose, either the first electrode 101 or the secondelectrode 103 or both has/have a light-transmitting property.

The use of the light-emitting element described in this embodiment makesit possible to manufacture a passive matrix light-emitting device or anactive matrix light-emitting device in which the driving of thelight-emitting element is controlled by a thin film transistor (TFT).

Note that there is no particular limitation on the structure of the TFTin the case of manufacturing an active matrix light-emitting device. Forexample, a staggered TFT or an inverted staggered TFT can be used asappropriate. Further, a driver circuit formed over a TFT substrate maybe formed using both of an n-channel TFT and a p-channel TFT or onlyeither an n-channel TFT or a p-channel TFT. Furthermore, there is noparticular limitation on the crystallinity of a semiconductor film usedfor the TFT. For example, the semiconductor film can be an amorphoussemiconductor film, a crystalline semiconductor film, an oxidesemiconductor film, or the like.

The light-emitting element of this embodiment contains theorganometallic complex according to one embodiment of the presentinvention, which emits red light with high color purity, in thelight-emitting layer 113. As a result, the light-emitting element emitsred light with high color purity.

The structure described in this embodiment can be combined with thestructure described in Embodiment 1 as appropriate.

Embodiment 3

The light-emitting element which is one embodiment of the presentinvention may include a plurality of light-emitting layers. A pluralityof light-emitting layers may be provided so that each of thelight-emitting layers emits light, thereby obtaining a combination oflight emission from the plurality of layers. Thus, white light emissioncan be obtained, for example. This embodiment shows a mode of alight-emitting element including a plurality of light-emitting layers,with reference to FIG. 2.

As illustrated in FIG. 2, the light-emitting element is provided with afirst light-emitting layer 213 and a second light-emitting layer 215between a first electrode 201 and a second electrode 203. A separationlayer 214 is preferably formed between the first light-emitting layer213 and the second light-emitting layer 215.

Now, light emission of the element is described. By applying a voltagesuch that the potential of the first electrode 201 is higher than thepotential of the second electrode 203, current flows between the firstelectrode 201 and the second electrode 203. As a result, holes andelectrons recombine in any of the first light-emitting layer 213, thesecond light-emitting layer 215, and the separation layer 214. Generatedexcitation energy is distributed to both the first light-emitting layer213 and the second light-emitting layer 215 to excite a firstlight-emitting substance contained in the first light-emitting layer 213and a second light-emitting substance contained in the secondlight-emitting layer 215. The excited first and second light-emittingsubstances emit light while relaxing to the ground state. Thus, thelight-emitting element can provide combination of light emission fromthe first light-emitting layer 213 and light emission from the secondlight-emitting layer 215.

The first light-emitting layer 213 contains the first light-emittingsubstance typified by a fluorescent compound such as perylene,2,5,8,11-tetra(tert-butyl)perylene (abbreviation: TBP), DPVB4,4′-bis[2-(N-ethylcarbazol-3-yl)vinyl]biphenyl (abbreviation: BCzVBi),BAlq, or bis(2-methyl-8-quinolinolato)galliumchloride (abbreviation:Gamq₂Cl); or a phosphorescent compound such asbis{2-[3,5-bis(trifluoromethyl)phenyl]pyridinato-N,C^(2′)}iridium(III)picolinate(abbreviation: Ir(CF₃ ppy)₂(pic)),bis[2-(4,6-difluorophenyl)pyridinato-N,C^(2′)]iridium(III)acetylacetonate(abbreviation: FIr(acac)), bis[2-(4,6-difluorophenyl)pyridinato-N,C^(2′)]iridium(III)picolinate (abbreviation: FIrpic), orbis[2-(4,6-difuluorophenyl)pyridinato-N,C^(2′)]iridium(III)tetra(1-pyrazolyl)borate(abbreviation: FIr6), which emits light having a peak at 450 nm to 510nm in an emission spectrum (i.e., blue light to blue green light).

In addition, when the first light-emitting substance is a fluorescentcompound, the first light-emitting layer 213 preferably has a structurein which a substance that has higher singlet excitation energy than thefirst light-emitting substance is used as a first host and the firstlight-emitting substance is dispersed as a guest. Further, when thefirst light-emitting substance is a phosphorescent compound, the firstlight-emitting layer 213 preferably has a structure in which a substancethat has higher triplet excitation energy than the first light-emittingsubstance is used as a first host and the first light-emitting substanceis dispersed as a guest. As the first host, DNA, t-BuDNA, or the likecan be used in addition to the above-described NPB, CBP, TCTA, and thelike. Note that the singlet excitation energy is an energy differencebetween a ground state and a singlet excited state. In addition, thetriplet excitation energy is an energy difference between a ground stateand a triplet excited state.

On the other hand, the second light-emitting layer 215 contains theorganometallic complex which is one embodiment of the present inventionand can emit red light. The second light-emitting layer 215 may have astructure similar to the light-emitting layer 113 described inEmbodiment 2.

Specifically, the separation layer 214 can be formed using TPAQn, NPB,CBP, TCTA, Znpp₂, ZnBOX or the like described above. The thus providedseparation layer 214 can prevent a defect that emission intensity of oneof the first light-emitting layer 213 and the second light-emittinglayer 215 is stronger than that of the other. Note that the separationlayer 214 is not necessarily provided and may be provided as appropriateso that the ratio in emission intensity of the first light-emittinglayer 213 and the second light-emitting layer 215 can be adjusted.

In this embodiment, the second light-emitting layer 215 is formed usingthe organometallic complex according to one embodiment of the presentinvention and the first light-emitting layer 213 is formed using any oneof the first light-emitting substances listed above. Alternatively, thefirst light-emitting layer 213 may be formed using the organometalliccomplex according to one embodiment of the present invention and thesecond light-emitting layer 215 may be formed using any one of the firstlight-emitting substances.

Although this embodiment shows the light-emitting element in which twolight-emitting layers are provided as illustrated in FIG. 2, the numberof the light-emitting layers is not limited to two, and may be three forexample. In addition, light emission from each light-emitting layer maybe mixed. As a result, white light emission can be obtained, forexample.

Note that the first electrode 201 may have a structure similar to thatof the first electrode 101 described in Embodiment 2. In addition, thesecond electrode 203 may also have a structure similar to that of thesecond electrode 103 described in Embodiment 2.

Further, this embodiment shows a hole-injection layer 211, ahole-transport layer 212, an electron-transport layer 216, and anelectron-injection layer 217 as illustrated in FIG. 2. As for structuresof these layers, the structures of the respective layers described inEmbodiment 2 may be applied. However, these layers are not necessarilyprovided and may be provided as appropriate according to elementcharacteristics.

Note that the structure described in this embodiment can be combinedwith the structure described in Embodiment 1 or 2 as appropriate.

Embodiment 4

This embodiment shows, as one embodiment of the present invention, astructure of a light-emitting element including a plurality of EL layers(hereinafter, such a light-emitting element is referred to as astacked-type element) with reference to FIG. 3. This light-emittingelement is a stacked-type light-emitting element including a pluralityof EL layers (a first EL layer 302 and a second EL layer 303) between afirst electrode 301 and a second electrode 304. Although this embodimentshows the case of two EL layers, three or more EL layers may beemployed.

In this embodiment, the first electrode 301 functions as an anode, andthe second electrode 304 functions as a cathode. Note that the firstelectrode 301 and the second electrode 304 can have structures similarto those described in Embodiment 2.

In addition, although the plurality of EL layers (the first EL layer 302and the second EL layer 303) may have structures similar to thosedescribed in Embodiment 2, any of the EL layers may have a structuresimilar to that described in Embodiment 2. In other words, thestructures of the first EL layer 302 and the second EL layer 303 may bethe same or different from each other and can be similar to thosedescribed in Embodiment 2.

Further, a charge generation layer 305 is provided between the pluralityof EL layers (the first EL layer 302 and the second EL layer 303). Thecharge generation layer 305 has a function of injecting electrons intoone of the EL layers and injecting holes into the other of the EL layerswhen a voltage is applied between the first electrode 301 and the secondelectrode 304. In this embodiment, when a voltage is applied such thatthe potential of the first electrode 301 is higher than that of thesecond electrode 304, the charge generation layer 305 injects electronsinto the first EL layer 302 and injects holes into the second EL layer303.

Note that the charge generation layer 305 preferably has alight-transmitting property in terms of light extraction efficiency.Further, the charge generation layer 305 functions even if it has lowerconductivity than the first electrode 301 or the second electrode 304.

The charge generation layer 305 may have either a structure in which anelectron acceptor (acceptor) is added to an organic compound having ahigh hole-transport property or a structure in which an electron donor(donor) is added to an organic compound having a high electron-transportproperty. Alternatively, both of these structures may be stacked.

In the case of the structure in which an electron acceptor is added toan organic compound having a high hole-transport property, as theorganic compound having a high hole-transport property, for example, anaromatic amine compound such as NPB, TPD, TDATA, MTDATA, or4,4′-bis[N-(spiro-9,9′-bifluoren-2-yl)-N-phenylamino]biphenyl(abbreviation: BSPB), or the like can be used. The substances mentionedhere are mainly ones that have a hole mobility of 10⁻⁶ cm²/V·s orhigher. However, another substance may be used as long as the substanceis an organic compound having a higher hole-transport property than anelectron-transport property.

Further, as the electron acceptor,7,7,8,8-tetracyano-2,3,5,6-tetrafluoroquinodimethane (abbreviation:F₄-TCNQ), chloranil, or the like can be used. Alternatively, atransition metal oxide can be used. Further alternatively, an oxide ofmetals that belong to Group 4 to Group 8 of the periodic table can beused. Specifically, it is preferable to use vanadium oxide, niobiumoxide, tantalum oxide, chromium oxide, molybdenum oxide, tungsten oxide,manganese oxide, or rhenium oxide because the electron-acceptingproperty is high. Among these, molybdenum oxide is especially preferablebecause it is stable in the air and its hygroscopic property is low andis easily treated.

On the other hand, in the case of the structure in which an electrondonor is added to an organic compound having a high electron-transportproperty, the organic compound having a high electron-transport propertycan be used; for example, a metal complex having a quinoline skeleton ora benzoquinoline skeleton, such as Alq, Almq₃, BeBq₂, or BAlq, or thelike can be used. Alternatively, it is possible to use a metal complexhaving an oxazole-based ligand or a thiazole-based ligand, such asZn(BOX)₂ or Zn(BTZ)₂. Further alternatively, instead of a metal complex,it is possible to use PBD, OXD-7, TAZ, BPhen, BCP, or the like. Thesubstances mentioned here are mainly ones that have an electron mobilityof 10⁻⁶ cm²/V·s or higher. Note that another substance may be used aslong as the substance is an organic compound having a higherelectron-transport property than a hole-transport property.

As the electron donor, it is possible to use an alkali metal, analkaline earth metal, a rare earth metal, a metal belonging to Group 13of the periodic table, or an oxide or carbonate thereof. Specifically,it is preferable to use lithium (Li), cesium (Cs), magnesium (Mg),calcium (Ca), ytterbium (Yb), indium (In), lithium oxide, cesiumcarbonate, or the like. Alternatively, an organic compound such astetrathianaphthacene may be used as the electron donor.

Note that forming the charge generation layer 305 by using any of theabove materials can suppress an increase in drive voltage caused by thestack of the EL layers.

Although this embodiment shows the light-emitting element having two ELlayers, the present invention can be similarly applied to alight-emitting element in which three or more EL layers are stacked. Asin the light-emitting element according to this embodiment, when acharge generation layer is interposed between a plurality of EL layersbetween a pair of electrodes, light emission in a high luminance regioncan be obtained. Since the current density can be kept low, the elementcan have a long lifetime. When the light-emitting element is applied forillumination, voltage drop due to resistance of an electrode materialcan be reduced, thereby achieving homogeneous light emission in a largearea. Moreover, it is possible to achieve a light-emitting device of lowpower consumption, which can be driven at a low voltage.

By making the EL layers emit light of different colors from each other,the light-emitting element can provide light emission of a desired coloras a whole. For example, by forming a light-emitting element having twoEL layers such that the emission color of the first EL layer and theemission color of the second EL layer are complementary colors, thelight-emitting element can provide white light emission as a whole. Notethat the word “complementary” means color relationship in which anachromatic color is obtained when colors are mixed. That is, whencomplementary colored light emitted from substances is mixed,white-light emission can be obtained.

Further, the same can be applied to a light-emitting element havingthree EL layers. For example, the light-emitting element as a whole canprovide white light emission when the emission color of the first ELlayer is red, the emission color of the second EL layer is green, andthe emission color of the third EL layer is blue.

Note that the structure described in this embodiment can be combinedwith any of the structures described in Embodiments 1 to 3 asappropriate.

Embodiment 5

This embodiment shows, as one embodiment of the present invention, anmode of a light-emitting element in which an organometallic complex isused as a sensitizer, with reference to FIG. 1.

FIG. 1 illustrates a light-emitting element in which the EL layer 102including the light-emitting layer 113 is interposed between the firstelectrode 101 and the second electrode 103. The light-emitting layer 113contains the organometallic complex which is one embodiment of thepresent invention and a fluorescent compound which can emit light havinga longer wavelength than the organometallic complex.

In such a light-emitting element, holes injected from the firstelectrode 101 side and electrons injected from the second electrode 103side recombine in the light-emitting layer 113 to bring the fluorescentcompound into an excited state. The excited fluorescent compound emitslight while relaxing to the ground state. In this case, theorganometallic complex which is one embodiment of the present inventionacts as a sensitizer for the fluorescent compound to increase the numberof molecules of fluorescent compounds in singlet excited states. In theabove manner, the organometallic complex which is one embodiment of thepresent invention can be used as a sensitizer so as to achieve alight-emitting element with high emission efficiency. Note that in thelight-emitting element of this embodiment, the first electrode 101functions as an anode and the second electrode 103 function as acathode.

The light-emitting layer 113 contains the organometallic complex whichis one embodiment of the present invention and the fluorescent compoundwhich can emit light having a longer wavelength than the organometalliccomplex. In the light-emitting layer 113, it is preferable that asubstance having higher triplet excitation energy than theorganometallic complex and higher singlet excitation energy than thefluorescent compound be used as a host and the organometallic complexand the fluorescent compound be dispersed as a guest.

Note that there is no particular limitation on the substance used fordispersing the organometallic complex and the fluorescent compound(i.e., host), and the substances given as examples of the host inEmbodiment 2, or the like can be used.

Although there is no particular limitation on the fluorescent compound,it is preferable to use a compound which emits red light to infraredlight, such as4-dicyanomethylene-2-isopropyl-6-[2-(1,1,7,7-tetramethyljulolidin-9-yl)ethenyl]-4H-pyran (abbreviation: DCJTI), magnesium phthalocyanine, magnesiumporphyrin, phthalocyanine, or the like.

Note that the first electrode 101 and the second electrode 103 describedin this embodiment may have structures similar to those of the firstelectrode and the second electrode described in Embodiment 2,respectively.

As illustrated in FIG. 1, the hole-injection layer 111, thehole-transport layer 112, the electron-transport layer 114, and theelectron-injection layer 115 are provided in this embodiment; structuresthereof may be those of the respective layers described in Embodiment 2.However, these layers are not necessarily provided and may be providedas appropriate according to element characteristics.

The above-described light-emitting element can emit light with highefficiency by use of the organometallic complex which is one embodimentof the present invention as a sensitizer.

Note that the structure described in this embodiment can be combinedwith any of the structures described in Embodiments 1 to 4 asappropriate.

Embodiment 6

This embodiment shows, as one embodiment of the present invention, apassive matrix light-emitting device and an active matrix light-emittingdevice each of which is a light-emitting device fabricated using alight-emitting element.

FIGS. 4A to 4D and FIG. 5 illustrate examples of passive matrixlight-emitting devices.

The passive matrix (also called simple matrix) light-emitting deviceexemplified in this embodiment includes a plurality of anodes arrangedin stripes (in stripe form) and a plurality of cathodes arranged instripes. The plurality of anodes are provided to intersect with theplurality of cathodes, and intersecting portions arranged in matrix formpixel portions. In each of the intersecting portions of the anodes andthe cathodes, a light-emitting layer is interposed therebetween.Accordingly, voltage application between one anode and one cathodecauses a light-emitting layer at the intersecting portion (i.e., apixel) to emit light.

FIGS. 4A to 4C are top views of a pixel portion. FIG. 4D is across-sectional view taken along the chain line A-N in FIGS. 4A to 4C.Note that there is no illustration of a structure in which thelight-emitting element is sealed.

An insulating layer 402 is provided as a base insulating layer over asubstrate 401; however, the base insulating layer is not necessarilyprovided. A plurality of first electrodes 403 are provided over theinsulating layer 402 (see FIG. 4D). Note that the plurality of firstelectrodes 403 are arranged in stripes at regular intervals over theinsulating layer 402 (see FIG. 4A).

In addition, a partition 404 having openings 405 each corresponding to apixel is provided over the first electrodes 403. The partition 404having the openings 405 is formed using an insulating material (aphotosensitive or nonphotosensitive organic material (e.g., polyimide,acrylic, polyamide, polyimide amide, resist, or benzocyclobutene) or anSOG film (e.g., a SiO_(x) film containing an alkyl group)). Note thatthe openings 405 each corresponding to a pixel serve as light-emittingregions (FIG. 4B).

Over the partition 404 having the openings 405, a plurality of inverselytapered partitions 406 which are parallel to each other is provided tointersect with the first electrodes 403 (FIG. 4C). The inversely taperedpartitions 406 are formed by a photolithography method using a positivephotosensitive resin, portion of which unexposed to light remains as apattern, and by adjustment of the amount of light exposure or the lengthof development time so that a lower portion of a pattern is etched more.

After the inversely tapered partitions 406 are formed as illustrated inFIG. 4C, EL layers 407 and second electrodes 408 are sequentially formedas illustrated in FIG. 4D. The total thickness of the partition 404having the openings 405 and the inversely tapered partition 406 is setto be larger than the total thickness of the EL layer 407 and the secondelectrode 408; thus, as illustrated in FIG. 4D, EL layers 407 and secondelectrodes 408 which are divided into plural regions are formed. Notethat the plurality of divided regions are electrically isolated from oneanother.

The second electrodes 408 are electrodes in stripe form that areparallel to each other and extend along a direction intersecting withthe first electrodes 403. Note that parts of a layer for forming the ELlayers 407 and parts of a conductive layer for forming the secondelectrodes 408 are also formed over the inversely tapered partitions406; however, these parts are separated from the EL layers 407 and thesecond electrodes 408.

Note that in this embodiment, the first electrode 403 may function as ananode and the second electrode 408 may function as a cathode, or viceversa. Note that a stacked structure including the EL layer 407 may beadjusted as appropriate in accordance with the polarity of theelectrode.

Further, if necessary, a sealing material such as a sealing can or aglass substrate may be attached to the substrate 401 for sealing with anadhesive such as a sealant, so that the light-emitting element is placedin the sealed space. Thereby, deterioration of the light-emittingelement can be prevented. The sealed space may be filled with filler ora dry inert gas. Further, a desiccant or the like may be put between thesubstrate and the sealing material in order to prevent deterioration ofthe light-emitting element due to moisture or the like. The desiccantremoves a minute amount of moisture, thereby achieving sufficientdesiccation. The desiccant may be a substance which absorbs moisture bychemical adsorption such as an oxide of an alkaline earth metal astypified by calcium oxide or barium oxide. Additionally, a substancewhich adsorbs moisture by physical adsorption such as zeolite or silicagel may be used as well, as a desiccant.

FIG. 5 is a top view of the case where the passive matrix light-emittingdevice illustrated in FIGS. 4A to 4D is mounted with an FPC and thelike.

As illustrated in FIG. 5, in a pixel portion forming an image display,scanning lines and data lines intersect with each other so that they areorthogonal to each other.

Here, the substrate 401, the first electrode 403, the second electrode408, and the inversely tapered partition 406 in FIGS. 4A to 4Dcorrespond to a substrate 501, a scan line 503, a data line 508, and apartition 506 in FIG. 5, respectively. The EL layers 407 in FIGS. 4A to4D are interposed between the data lines 508 and the scan lines 503, andan intersection portion indicated by a region 505 corresponds to onepixel.

Note that the scan lines 503 are electrically connected at their ends toconnection wirings 509, and the connection wirings 509 are connected toan FPC 511 b through an input terminal 510. In addition, the data lines508 are connected to an FPC 511 a through the input terminal 512.

If necessary, a polarizing plate, a circularly polarizing plate(including an elliptically polarizing plate), a retardation plate (aquarter-wave plate or a half-wave plate), or an optical film such as acolor filter may be provided as appropriate over a light-emittingsurface. Further, the polarizing plate or the circularly polarizingplate may be provided with an anti-reflection film. For example,anti-glare treatment can be performed so that reflected light can bediffused by projections and depressions on the surface to reduce theglare.

Although FIG. 5 illustrates an example in which a driver circuit is notprovided over the substrate, an IC chip including a driver circuit maybe mounted over the substrate.

When the IC chip is mounted, a data line side IC and a scan line sideIC, in each of which a driver circuit for transmitting a signal to apixel portion is formed, are mounted on the periphery of the pixelportion (outside the pixel portion) by a COG method. The mounting may beperformed using a TCP or a wire bonding method other than the COGmethod. The TCP is a TAB tape mounted with the IC, and the TAB tape isconnected to a wiring over an element formation substrate to mount theIC. Each of the data line side IC and the scan line side IC may beformed using a silicon substrate, or may be formed using a glasssubstrate, a quartz substrate, or a plastic substrate over which adriver circuit is formed using TFTs.

Next, an example of an active matrix light-emitting device is describedwith reference to FIGS. 6A and 6B. Note that FIG. 6A is a top viewillustrating a light-emitting device and FIG. 6B is a cross-sectionalview taken along the chain line A-A′ in FIG. 6A. The active matrixlight-emitting device according to this embodiment includes a pixelportion 602 provided over an element substrate 601, a driver circuitportion (a source side driver circuit) 603, and a driver circuit portion(a gate side driver circuit) 604. The pixel portion 602, the drivercircuit portion (source side driver circuit) 603, and the driver circuitportion (gate side driver circuit) 604 are sealed between the elementsubstrate 601 and the sealing substrate 606 by a sealant 605.

In addition, there is provided a lead wiring 607 over the elementsubstrate 601. The lead wiring 607 is provided for connecting anexternal input terminal through which a signal (e.g., a video signal, aclock signal, a start signal, and a reset signal) or a potential fromthe outside is transmitted to the driver circuit portion (source sidedriver circuit) 603 and the driver circuit portion (gate side drivercircuit) 604. Here is shown an example in which a flexible printedcircuit (FPC) is provided as the external input terminal. Although anFPC 608 is illustrated alone, this FPC may be provided with a printedwiring board (PWB). The light-emitting device in this specificationincludes, in its category, not only the light-emitting device itself butalso the light-emitting device to which the FPC or the FPC provided withthe PWB is attached.

Next, a cross-sectional structure is described with reference to FIG.6B. The driver circuit portion and the pixel portion are formed over theelement substrate 601; here are illustrated the driver circuit portion(source side driver circuit) 603 which is the source driver circuit andthe pixel portion 602.

The driver circuit portion (source side driver circuit) 603 is anexample where a CMOS circuit is formed, which is a combination of ann-channel TFT 609 and a p-channel TFT 610. Note that a circuit includedin the driver circuit portion may be formed using various CMOS circuits,PMOS circuits, or NMOS circuits. Although this embodiment shows a driverintegrated type in which the driver circuit is formed over thesubstrate, the driver circuit is not necessarily formed over thesubstrate, and the driver circuit can be formed outside, not over thesubstrate.

The pixel portion 602 is formed of a plurality of pixels each of whichincludes a switching TFT 611, a current control TFT 612, and an anode613 which is electrically connected to a wiring (a source electrode or adrain electrode) of the current control TFT 612. Note that an insulator614 is formed to cover end portions of the anode 613. In thisembodiment, the insulator 614 is formed using a positive photosensitiveacrylic resin.

The insulator 614 preferably has a curved surface with curvature at anupper end portion or a lower end portion thereof in order to obtainfavorable coverage by a film which is to be stacked over the insulator614. For example, in the case of using a positive photosensitive acrylicresin as a material for the insulator 614, the insulator 614 preferablyhas a curved surface with a curvature radius (0.2 μm to 3 μm) at theupper end portion. Note that the insulator 614 can be formed usingeither a negative photosensitive material that becomes insoluble in anetchant by light irradiation or a positive photosensitive material thatbecomes soluble in an etchant by light irradiation. It is possible touse, without limitation to an organic compound, either an organiccompound or an inorganic compound such as silicon oxide or siliconoxynitride.

An EL layer 615 and a cathode 616 are stacked over the anode 613. Notethat it is preferable that the anode 613 be formed using an indium tinoxide film, and that a wiring of the current-controlling TFT 612connected to the anode 613 be formed using a stacked film of a titaniumnitride film and a film containing aluminum as its main component or astacked film of a titanium nitride film, a film containing aluminum asits main component, and a titanium nitride film. This structure achieveslow resistance of the wiring and favorable ohmic contact with the indiumtin oxide film. Although not illustrated in FIGS. 6A and 6B, the cathode616 is electrically connected to an FPC 608 which is an external inputterminal.

The EL layer 615 includes at least a light-emitting layer. The EL layer615 is provided with, in addition to the light-emitting layer, ahole-injection layer, a hole-transport layer, an electron-transportlayer, or an electron-injection layer, as appropriate. A light-emittingelement 617 is formed of a stacked structure of the anode 613, the ELlayer 615, and the cathode 616.

Although the cross-sectional view of FIG. 6B illustrates only onelight-emitting element 617, a plurality of light-emitting elements arearranged in matrix in the pixel portion 602. Light-emitting elementswhich provide three kinds of light emission (R, G and B) are selectivelyformed in the pixel portion 602, whereby a light-emitting device capableof full color display can be fabricated. Alternatively, a light-emittingdevice which is capable of full color display may be fabricated by acombination with color filters.

Further, the sealing substrate 606 is attached to the element substrate601 with the sealant 605, whereby a light-emitting element 617 isprovided in a space 618 surrounded by the element substrate 601, thesealing substrate 606, and the sealant 605. The space 618 may be filledwith an inert gas (such as nitrogen or argon), or the sealant 605.

An epoxy based resin is preferably used for the sealant 605. It isdesirable that materials used for the sealant 605 do not transmitmoisture or oxygen as much as possible. As the sealing substrate 606, aplastic substrate formed of FRP (fiberglass-reinforced plastics), PVF(polyvinyl fluoride), polyester, or acrylic can be used instead of aglass substrate or a quartz substrate.

As described above, an active matrix light-emitting device can beobtained.

Note that the structure described in this embodiment can be combinedwith any of the structures described in Embodiments 1 to 5 asappropriate.

Embodiment 7

This embodiment shows, with reference to FIGS. 7A to 7E and FIG. 8,examples of a variety of electronic devices and lighting devices thatare completed by using any light-emitting device which is one embodimentof the present invention.

Examples of the electronic devices to which the light-emitting device isapplied include television sets (also referred to as televisions ortelevision receivers), monitors of computers or the like, cameras suchas digital cameras or digital video cameras, digital photo frames,cellular phones (also referred to as mobile phones or cellular phonesets), portable game consoles, portable information terminals, audioreproducing devices, large game machines such as pachinko machines, andthe like. Specific examples of these electronic devices and lightingdevice are illustrated in FIGS. 7A to 7E.

FIG. 7A illustrates an example of a television device. In a televisiondevice 7100, a display portion 7103 is incorporated in a housing 7101.Images can be displayed by the display portion 7103, and thelight-emitting device can be used for the display portion 7103. Inaddition, here, the housing 7101 is supported by a stand 7105.

The television device 7100 can be operated by an operation switch of thehousing 7101 or a separate remote controller 7110. With operation keys7109 of the remote controller 7110, channels and volume can becontrolled and images displayed on the display portion 7103 can becontrolled. Further, the remote controller 7110 may be provided with adisplay portion 7107 for displaying data output from the remotecontroller 7110.

Note that the television device 7100 is provided with a receiver, amodem, and the like. With the use of the receiver, general televisionbroadcasting can be received. Moreover, when the display device isconnected to a communication network with or without wires via themodem, one-way (from a sender to a receiver) or two-way (between asender and a receiver or between receivers) information communicationcan be performed.

FIG. 7B illustrates a computer, which includes a main body 7201, ahousing 7202, a display portion 7203, a keyboard 7204, an externalconnection port 7205, a pointing device 7206, and the like. Thiscomputer is manufactured by using a light-emitting device for thedisplay portion 7203.

FIG. 7C illustrates a portable game machine, which includes twohousings, a housing 7301 and a housing 7302, which are connected with ajoint portion 7303 so that the portable game machine can be opened orfolded. A display portion 7304 is incorporated in the housing 7301 and adisplay portion 7305 is incorporated in the housing 7302. In addition,the portable game machine illustrated in FIG. 7C includes a speakerportion 7306, a recording medium insertion portion 7307, an LED lamp7308, an input means (an operation key 7309, a connection terminal 7310,a sensor 7311 (a sensor having a function of measuring force,displacement, position, speed, acceleration, angular velocity,rotational frequency, distance, light, liquid, magnetism, temperature,chemical substance, sound, time, hardness, electric field, current,voltage, electric power, radiation, flow rate, humidity, gradient,oscillation, odor, or infrared rays), or a microphone 7312), and thelike. It is needless to say that the structure of the portable gamemachine is not limited to the above as long as the light-emitting deviceis used for at least either the display portion 7304 or the displayportion 7305, or both, and can include other accessories arbitrarily.The portable game machine illustrated in FIG. 7C has a function ofreading out a program or data stored in a storage medium to display iton the display portion, and a function of sharing information withanother portable game machine by wireless communication. The portablegame machine illustrated in FIG. 7C can have a variety of functionswithout limitation to the above.

FIG. 7D illustrates an example of a cellular phone. The cellular phone7400 is provided with a display portion 7402 incorporated in a housing7401, operation buttons 7403, an external connection port 7404, aspeaker 7405, a microphone 7406, and the like. Note that the cellularphone 7400 is manufactured using a light-emitting device for the displayportion 7402.

When the display portion 7402 of the cellular phone 7400 illustrated inFIG. 7D is touched with a finger or the like, data can be input into thecellular phone 7400. Further, operations such as making calls andcomposing e-mails can be performed by touching the display portion 7402with a finger or the like.

There are mainly three screen modes of the display portion 7402. Thefirst mode is a display mode mainly for displaying images. The secondmode is an input mode mainly for inputting data such as text. The thirdmode is a display-and-input mode in which two modes of the display modeand the input mode are combined.

For example, in the case of making a call or composing an e-mail, a textinput mode mainly for inputting text is selected for the display portion7402 so that text displayed on a screen can be inputted. In that case,it is preferable to display a keyboard or number buttons on almost allthe area of the screen of the display portion 7402.

When a detection device including a sensor for detecting inclination,such as a gyroscope or an acceleration sensor, is provided inside thecellular phone 7400, display on the screen of the display portion 7402can be automatically changed by determining the orientation of thecellular phone 7400 (whether the cellular phone is placed horizontallyor vertically for a landscape mode or a portrait mode).

The screen modes are switched by touching the display portion 7402 oroperating the operation buttons 7403 of the housing 7401. Alternatively,the screen modes can be switched depending on kinds of images displayedon the display portion 7402. For example, when a signal of an imagedisplayed on the display portion is a signal of moving image data, thescreen mode is switched to the display mode. When the signal is a signalof text data, the screen mode is switched to the input mode.

Moreover, in the input mode, when input by touching the display portion7402 is not performed within a specified period while a signal detectedby an optical sensor in the display portion 7402 is detected, the screenmode may be controlled so as to be switched from the input mode to thedisplay mode.

The display portion 7402 may function as an image sensor. For example,an image of a palm print, a fingerprint, or the like is taken bytouching the display portion 7402 with the palm or the finger, wherebypersonal authentication can be performed. Further, by providing abacklight or a sensing light source which emits a near-infrared light inthe display portion, an image of a finger vein, a palm vein, or the likecan be taken.

FIG. 7E illustrates a desk lamp including a lighting portion 7501, ashade 7502, an adjustable arm 7503, a support 7504, a base 7505, and apower supply 7506. The desk lamp is manufactured using a light-emittingdevice for the lighting portion 7501. Note that the lighting deviceincludes a ceiling light, a wall light, and the like.

FIG. 8 illustrates an example in which the light-emitting device is usedfor an indoor lighting device 801. Since the light-emitting device canalso have a large area, the light-emitting device can be used as alighting device having a large area. Alternatively, the light-emittingdevice can be used as a roll-type lighting device 802. Note that asillustrated in FIG. 8, a desk lamp 803 described with reference to FIG.7E may be used together in a room provided with the indoor lightingdevice 801.

As described above, electronic devices and lighting devices can beobtained by application of the light-emitting device. The light-emittingdevice has a remarkably wide application range, and can be applied toelectronic devices in various fields.

Note that the structure described in this embodiment can be combinedwith any of the structures described in Embodiments 1 to 6 asappropriate.

EXAMPLE 1 Synthesis Example

Example 1 shows a method of synthesizing(acetylacetonato)bis[3,5-dimethyl-2-(3-diphenylaminophenyl)pyrazinato]iridium(III)(abbreviation: [Ir(dm5dpappr)₂(acac)]), which is the organometalliccomplex according to one embodiment of the present invention representedby the structural formula (100) in Embodiment 1. The structure of[Ir(dm5dpappr)₂(acac)] is shown below.

Step 1: Synthesis of 2-(3-Diphenylaminophenyl)-1,3,2-dioxaborolane

First, 0.45 g of magnesium and 5 ml of THF were suspended, and a tinyamount of 1,2-dibromoethane was added to the obtained suspension. Amixed solution of 3.0 g of 3-bromo-N,N-diphenylaniline and 30 mL of THFwas dripped to this suspension, and the mixture was stirred while beingheated under reflux for 1.5 hours to cause a reaction. After thereaction, the solution which was naturally cooled to room temperaturewas cooled to −78° C., and 1.95 g of trimethyl borate was added thereto.The mixture was stirred while the temperature was increased to roomtemperature to cause a reaction. After the reaction, the solution wasconcentrated, and 4.8 mL of ethylene glycol and 30 mL of toluene wereadded to the obtained residue. The mixture was stirred while beingheated under reflux for 12 hours to cause a reaction. After thereaction, the solution was filtered and the obtained filtrate wasconcentrated, so that a while solid was obtained (88% yield). Thesynthesis scheme of Step 1 is shown by (a-1).

Step 2: Synthesis of 3,5-Dimethyl-2-(3-diphenylaminophenyl)pyrazine(abbreviation: Hdm5dpappr)

Next, there were put 0.39 g of 2-chloro-3,5-dimethylpyrazine, 0.87 g of2-(3-diphenylaminophenyl)-1,3,2-dioxaborolane which was obtained in Step1, 0.30 g of sodium carbonate, 0.013 g ofbis(triphenylphosphine)palladium(II)dichloride (abbreviation:Pd(PPh₃)₂Cl₂), 10 mL of water, and 10 mL of acetonitrile in a recoveryflask equipped with a reflux pipe. The air in the flask was thenreplaced by argon. This reaction container was heated by microwaveirradiation (2.45 GHz, 100 W) for 20 minutes. After that, the reactioncontainer was cooled to 50° C. or lower. Then, water was added to thereaction solution, and the organic layer was subjected to extractionwith dichloromethane. The obtained organic layer was washed with waterand dried with magnesium sulfate. After the drying, the solution wasfiltered. The solvent of this solution was distilled, and the obtainedresidue was purified by silica gel column chromatography using a mixedsolvent of dichloromethane and ethyl acetate as a developing solvent,thereby obtaining the objective pyrazine derivative Hdm5dpappr (whitepowder, 11% yield). Note that the microwave irradiation was performedusing a microwave synthesis system (Discover, produced by CEMCorporation). The synthesis scheme of Step 2 is shown by (b-1).

Step 3: Synthesis ofDi-μ-chloro-bis{3,5-dimethyl-2-(3-diphenylaminophenyl)pyrazinato}iridium(III)](abbreviation: [ft(dm5dpappr)₂Cl]₂)

Next, there were put 3 mL of 2-ethoxyethanol, 1 mL of water, 0.11 g ofHdm5dpappr obtained in Step 2, and 0.044 g of iridium chloride hydrate(IrCl₃.H₂O) (produced by Sigma-Aldrich Corp.) in a recovery flaskequipped with a reflux pipe. The air in the flask was replaced by argon.After that, the mixture was heated by microwave irradiation (2.45 GHz,100 W) for 20 minutes. Then, the reaction container was cooled to 50° C.or lower, and the reaction solution was filtered. The obtained filtratewas washed with ethanol, so that the binuclear complex[Ir(dm5dpappr)₂Cl]₂ was obtained as red powder (53% yield). Thesynthesis scheme of Step 3 is shown by (c-1).

Step 4: Synthesis of(Acetylacetonato)bis[3,5-dimethyl-2-(3-diphenylaminophenyl)pyrazinato]iridium(III)(abbreviation: [Ir(dm5dpappr)₂(acac)])]

Further, there were put 15 mL of 2-ethoxyethanol, 0.08 g of thebinuclear complex [Ir(dm5dpappr)₂Cl]₂ obtained in Step 3, 0.01 mL ofacetylacetone, and 0.04 g of sodium carbonate in a recovery flaskequipped with a reflux pipe. The air in the flask was replaced by argon.After that, the mixture was heated by microwave irradiation (2.45 GHz,100 VT) for 20 minutes. Then, the reaction container was cooled to 50°C. or lower, and the reaction solution was concentrated and dried. Theobtained residue was dissolved in dichloromethane, and filtration wasperformed to remove insoluble solids. The obtained filtrate wasconcentrated and recrystallization with dichloromethane was performed,so that the organometallic complex [Ir(dm5dpappr)₂(acac)] according toone embodiment of the present invention was obtained as dark red powder(81% yield). The synthesis scheme of Step 4 is shown by (d-1).

Results of analysis of the dark red powder obtained in Step 4 by nuclearmagnetic resonance spectrometry (¹H-NMR) are shown below. FIG. 9 showsthe ¹H-NMR chart. According to the results, it was found that theorganometallic complex [Ir(dm5dpappr)₂(acac)], one embodiment of thepresent invention represented by the structural formula (100), wasobtained in this example.

¹H-NMR. δ (CDCl₃): 1.85 (s, 6H), 2.62 (s, 6H), 2.73 (s, 6H), 5.26 (s,1H), 6.11 (d, 2H), 6.60 (dd, 2H), 6.92 (m, 4H), 7.05 (m, 6H), 7.19 (m,10H), 7.65 (d, 2H), 8.29 (s, 2H).

Next, [Ir(dm5dpappr)₂(acac)] was analyzed by ultraviolet-visible(UV-vis) absorption spectroscopy. The UV-vis spectrum was measured withan ultraviolet-visible spectrophotometer (V-550, produced by JASCOCorporation) using a dichloromethane solution (0.051 mmol/L) at roomtemperature. Further, an emission spectrum of [Ir(dm5dpappr)₂(acac)] wasmeasured. The emission spectrum was measured by a fluorescencespectrophotometer (FS920, produced by Hamamatsu Photonics Corporation)using a degassed dichloromethane solution (0.31 mmol/L) at a roomtemperature. FIG. 10 shows the measurement results. In FIG. 10, thehorizontal axis represents wavelength and the vertical axis representsabsorption intensity and emission intensity.

As shown in FIG. 10, the organometallic complex [Ir(dm5dpappr)₂(acac)]which is one embodiment of the present invention has a peak of emissionat 690 nm, and deep red light was observed from the dichloromethanesolution.

COMPARATIVE EXAMPLE Comparative Synthesis Example

Comparative Example shows a method of synthesizing(acetylacetonato)bis[3,5-dimethyl-2-(4-diphenylaminophenyl)pyrazinato]iridium(III)(abbreviation: [Ir(dmdpappr)₂(acac)]). The structure of[Ir(dmdpappr)₂(acac)] is shown below.

Step 1: Synthesis of4,4,5,5-Tetramethyl-2-(4-diphenylaminophenyl)-1,3,2-dioxaborolane

First, there were put 1.0 g of 4-bromotriphenylamine, 0.86 g ofbis(pinacol)diborane, 1.8 g of potassium acetate, and 100 mL ofN,N-dimethylformamide (abbreviation: DMF) in a 200 mL three-neck flask.The air in the flask was replaced by nitrogen. Then, 150 mg of[1,1′-bis(diphenylphosphino)ferrocene]palladium(II)dichloridedichloromethane adduct (abbreviation: PdCl₂(dppf)) was added to thismixture, and the mixture was heated and stirred under a nitrogen streamat 80° C. for 30 hours to cause a reaction. After the reaction, about100 mL of water was added to the solution and the mixture was stirredfor 30 minutes. After the stirring, this suspension was separated, andan organic layer was fractionated. The resulting aqueous layer wassubjected to extraction with ethyl acetate and combined with thepreviously obtained organic layer, and washing was performed using waterand saturated saline in this order. After the washing, anhydratemagnesium sulfate was added to the solution for drying. After thedrying, the solution was gravity filtered and the resulting filtrate wasconcentrated to obtain a brown oily substance. This brown oily substancewas dissolved in hexane and the precipitated solid was removed byfiltration, thereby obtaining a filtrate. This filtrate was concentratedto obtain a pale yellow oily substance (96% yield). The synthesis schemeof Step 1 is shown by (a-2).

Step 2: Synthesis of 3,5-Dimethyl-2-(4-diphenylaminophenyl)pyrazine(abbreviation: Hdmdpappr)

Next, there were put 0.36 g of 2-chloro-3,5-dimethylpyrazine, 0.92 g of4,4,5,5-tetramethyl-2-(4-diphenylaminophenyl)-1,3,2-dioxaborolaneobtained in Step 1, 0.26 g of sodium carbonate, 0.011 g ofbis(triphenylphosphine)palladium(II)dichloride (abbreviation:Pd(PPh₃)₂Cl₂), 10 mL of water, and 10 mL of acetonitrile in a recoveryflask equipped with a reflux pipe. The air in the flask was replaced byargon. This reaction container was heated by microwave irradiation (2.45GHz, 100 W) for 20 minutes. After that, the reaction container wascooled to 50° C. or lower, water was added to the reaction solution, andthe organic layer was subjected to extraction with dichloromethane. Theobtained organic layer was washed with water and dried with magnesiumsulfate. After the drying, the solution was filtered. The solvent ofthis solution was distilled, and the obtained residue was purified bysilica gel column chromatography using a mixed solvent ofdichloromethane and ethyl acetate as a developing solvent, therebyobtaining the objective pyrazine derivative Hdmdpappr (white powder, 30%yield). Note that the microwave irradiation was performed using amicrowave synthesis system (Discover, produced by CEM Corporation). Thesynthesis scheme of Step 2 is shown by (b-2).

Step 3: Synthesis ofDi-μ-chloro-bis[bis{3,5-dimethyl-2-(4-diphenylaminophenyl)pyrazinato}iridium(III)](abbreviation: [Ir(dmdpappr)₂Cl]₂)

Next, there were put 6 mL of 2-ethoxyethanol, 2 mL of water, 0.26 g ofHdmdpappr obtained in Step 2, and 0.11 g of iridium chloride hydrate(IrCl₃.H₂O) (produced by Sigma-Aldrich Corp.) in a recovery flaskequipped with a reflux pipe. The air in the flask was replaced by argon.After that, the mixture was heated by microwave irradiation (2.45 GHz,100 W) for 20 minutes. Then, the reaction container was cooled to 50° C.or lower, and the reaction solution was filtered. The obtained residuewas washed with ethanol, so that a binuclear complex [Ir(dmdpappr)₂Cl]₂was obtained as ocher powder (74% yield). The synthesis scheme of Step 3is shown in (c-2).

Step 4: Synthesis of(Acetylacetonato)bis[3,5-dimethyl-2-(4-diphenylaminophenyl)pyrazinato]iridium(III)(abbreviation: [Ir(dmdpappr)₂(acac)])

Further, there were put 10 mL of 2-ethoxyethanol, 0.24 g of thebinuclear complex [Ir(dmdpappr)₂Cl]₂ obtained in Step 3, 0.040 mL ofacetylacetone, and 0.14 g of sodium carbonate in a recovery flaskequipped with a reflux pipe. The air in the flask was replaced by argon.After that, the mixture was heated by microwave irradiation (2.45 GHz,100 W) for 20 minutes. Then, the reaction container was cooled to 50° C.or lower, and the reaction solution was concentrated and dried. Theobtained residue was dissolved in dichloromethane, and filtration wasperformed to remove insoluble solids. The obtained filtrate wasconcentrated and the residue was purified by silica gel columnchromatography using ethyl acetate as a developing solvent, therebyobtaining [Ir(dmdpappr)₂(acac)] as red powder (8% yield). The synthesisscheme of Step 4 is shown by (d-2).

Results of analysis of the red powder obtained in Step 4 by nuclearmagnetic resonance spectrometry (¹H-NMR) are shown below. FIG. 11 showsthe ¹H-NMR chart. According to the results, it was found that[Ir(dmdpappr)₂(acac)] was obtained.

¹H-NMR. δ (CDCl₃): 1.81 (s, 6H), 2.42 (s, 6H), 2.82 (s, 6H), 5.20 (s,1H), 5.69 (d, 2H), 6.55 (dd, 2H), 6.95 (m, 12H), 7.15 (m, 8H), 7.60 (d,2H), 7.97 (s, 2H).

Next, [Ir(dmdpappr)₂(acac)] was analyzed by ultraviolet-visible (UV-vis)absorption spectroscopy. The UV-vis spectrum was measured with anultraviolet-visible spectrophotometer (V-550, produced by JASCOCorporation) using a dichloromethane solution (0.067 mmol/L) at roomtemperature. Further, an emission spectrum of [Ir(dmdpappr)₂(acac)] wasmeasured. The emission spectrum was measured by a fluorescencespectrophotometer (FS920, produced by Hamamatsu Photonics Corporation)using a degassed dichloromethane solution (0.40 mmol/L) at a roomtemperature. FIG. 12 shows the measurement results. In FIG. 12, thehorizontal axis represents wavelength and the vertical axis representsabsorption intensity and emission intensity.

As shown in FIG. 12, [Ir(dmdpappr)₂(acac)] has a peak of emission at 590nm, and orange light was observed from the dichloromethane solution.

This application is based on Japanese Patent Application serial no.2010-287239 filed with Japan Patent Office on Dec. 24, 2010, the entirecontents of which are hereby incorporated by reference.

What is claimed is:
 1. A light-emitting element comprising anorganometallic complex comprising a structure represented by a formula(G1),

wherein R¹ represents any of an alkyl group having 1 to 4 carbon atoms,an alkoxy group having 1 to 4 carbon atoms, and an alkoxycarbonyl grouphaving 1 to 5 carbon atoms, wherein R² and R³ independently representhydrogen or an alkyl group having 1 to 4 carbon atoms, wherein R⁴, R⁵,and R⁶ independently represent any of hydrogen, an alkyl group having 1to 4 carbon atoms, an alkoxy group having 1 to 4 carbon atoms, ahalogen, a trifluoromethyl group, and an aryl group having 6 to 12carbon atoms, wherein R⁷ and R⁸ independently represent an alkyl grouphaving 1 to 4 carbon atoms or an aryl group having 6 to 12 carbon atoms,and wherein M is iridium.
 2. The light-emitting element according toclaim 1, wherein the structure is represented by a formula (G2),


3. The light-emitting element according to claim 1, wherein thestructure is represented by a formula (G3),


4. An electronic device comprising a light-emitting device comprisingthe light-emitting element according to claim
 1. 5. A lighting devicecomprising a light-emitting device comprising the light-emitting elementaccording to claim
 1. 6. A light-emitting element comprising anorganometallic complex comprising a structure represented by a formula(G4),

wherein R¹ represents any of an alkyl group having 1 to 4 carbon atoms,an alkoxy group having 1 to 4 carbon atoms, and an alkoxycarbonyl grouphaving 1 to 5 carbon atoms, wherein R² and R³ independently representhydrogen or an alkyl group having 1 to 4 carbon atoms, wherein R⁴, R⁵,and R⁶ independently represent any of hydrogen, an alkyl group having 1to 4 carbon atoms, an alkoxy group having 1 to 4 carbon atoms, ahalogen, a trifluoromethyl group, and an aryl group having 6 to 12carbon atoms, wherein R⁷ and R⁸ independently represent an alkyl grouphaving 1 to 4 carbon atoms or an aryl group having 6 to 12 carbon atoms,wherein L represents any of formula (L1), formula (L2), formula (L3),formula (L4), formula (L5), formula (L6), formula (L7) and formula (L8):

wherein M is iridium, wherein n is 2, and wherein the monoanionic ligandis any of a monoanionic bidentate chelate ligand having a β-diketonestructure and a monoanionic bidentate chelate ligand having a carboxylgroup.
 7. The light-emitting element according to claim 6, wherein thestructure is represented by a formula (G6),


8. The light-emitting element according to claim 6, wherein themonoanionic ligand is selected from the group consisting of formula (L1)and formula (L2):


9. An electronic device comprising a light-emitting device comprisingthe light-emitting element according to claim
 6. 10. A lighting devicecomprising a light-emitting device comprising the light-emitting elementaccording to claim
 6. 11. A light-emitting element comprising anorganometallic complex comprising a structure represented by a formula(G4),

wherein R¹ represents any of an alkyl group having 1 to 4 carbon atoms,an alkoxy group having 1 to 4 carbon atoms, and an alkoxycarbonyl grouphaving 1 to 5 carbon atoms, wherein R² and R³ independently representhydrogen or an alkyl group having 1 to 4 carbon atoms, wherein R⁴, R⁵,and R⁶ independently represent any of hydrogen, an alkyl group having 1to 4 carbon atoms, an alkoxy group having 1 to 4 carbon atoms, ahalogen, a trifluoromethyl group, and an aryl group having 6 to 12carbon atoms, wherein R⁷ and R⁸ are bonded to each other through acarbon atom, an oxygen atom, a sulfur atom, or a nitrogen atom having amethyl group, to form a five-membered ring or a six-membered ring,wherein L represents any of formula (L1), formula (L2), formula (L3),formula (L4), formula (L5), formula (L6), formula (L7) and formula (L8):

wherein M is iridium, wherein n is 2, and wherein the monoanionic ligandis any of a monoanionic bidentate chelate ligand having a β-diketonestructure and a monoanionic bidentate chelate ligand having a carboxylgroup.
 12. The light-emitting element according to claim 10, wherein thestructure is represented by a formula (G6),


13. The light-emitting element according to claim 11, wherein themonoanionic ligand is selected from the group consisting of formula (L1)and formula (L2):


14. An electronic device comprising a light-emitting device comprisingthe light-emitting element according to claim
 11. 15. A lighting devicecomprising a light-emitting device comprising the light-emitting elementaccording to claim
 11. 16. A light-emitting element comprising anorganometallic complex comprising a structure represented by a formula(G7),

wherein R¹ represents any of an alkyl group having 1 to 4 carbon atoms,an alkoxy group having 1 to 4 carbon atoms, and an alkoxycarbonyl grouphaving 1 to 5 carbon atoms, wherein R² and R³ independently representhydrogen or an alkyl group having 1 to 4 carbon atoms, wherein R⁴, R⁵,and R⁶ independently represent any of hydrogen, an alkyl group having 1to 4 carbon atoms, an alkoxy group having 1 to 4 carbon atoms, ahalogen, a trifluoromethyl group, and an aryl group having 6 to 12carbon atoms, wherein R⁷ and R⁸ independently represent an alkyl grouphaving 1 to 4 carbon atoms or an aryl group having 6 to 12 carbon atoms,wherein M is iridium, and wherein n is
 2. 17. The light-emitting elementaccording to claim 16, wherein the structure is represented by a formula(G8),


18. The light-emitting element according to claim 16, wherein thestructure is represented by a formula (G9),


19. An electronic device comprising a light-emitting device comprisingthe light-emitting element according to claim
 16. 20. A lighting devicecomprising a light-emitting device comprising the light-emitting elementaccording to claim 16.